Changes in littler version 0.3.2 (2017-02-14)

• Changes in examples
  • New scripts getRStudioServer.r and getRStudioDesktop.r to download daily packages, currently defaults to Ubuntu amd64
  • New script c4c.r calling rhub::check_for_cran()
  • New script rd2md.r to convert Rd to markdown.
  • New script build.r to create a source tarball.
  • The installGitHub.r script now use package remotes (PR #44, #46)

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. Please report excessive re-aggregation in third-party for-profit settings.

KeePass: the popular alternative The most commonly used password-manager design pattern is to store passwords in a file that is encrypted and password-protected. The most popular free-software password manager of this kind is probably KeePass. An important feature of KeePass is the ability to auto-type passwords in forms, most notably in web browsers. This feature makes KeePass really easy to use, especially considering it also supports global key bindings to access passwords. KeePass databases are designed for simultaneous access by multiple users, for example, using a shared network drive. KeePass has a graphical interface written in C#, so it uses the Mono framework on Linux. A separate project, called KeePassX is a clean-room implementation written in C++ using the Qt framework. Both support the AES and Twofish encryption algorithms, although KeePass recently added support for the ChaCha20 cipher. AES key derivation is used to generate the actual encryption key for the database, but the latest release of KeePass also added using Argon2, which was the winner of the July 2015 password-hashing competition. Both programs are more or less equivalent, although the original KeePass seem to have more features in general. The KeePassX project has recently been forked into another project now called KeePassXC that implements a set of new features that are present in KeePass but missing from KeePassX like:

• auto-type on Linux, Mac OS, and Windows
• database merging which allows multi-user support
• using the web site's favicon in the interface

So far, the maintainers of KeePassXC seem to be open to re-merging the project "if the original maintainer of KeePassX in the future will be more active and will accept our merge and changes". I can confirm that, at the time of writing, the original KeePassX project now has 79 pending pull requests and only one pull request was merged since the last release, which was 2.0.3 in September 2016. While KeePass and derivatives allow multiple users to access the same database through the merging process, they do not support multi-party access to a single database. This may be a limiting factor for larger organizations, where you may need, for example, a different password set for different technical support team levels. The solution in this case is to use separate databases for each team, with each team using a different shared secret.

Pass: the standard password manager? I am currently using password-store, or pass, as a password manager. It aims to be "the standard Unix password manager". Pass is a GnuPG-based password manager that features a surprising number of features given its small size:

• copy-paste support
• Git integration
• multi-user/group support
• pluggable extensions (in the upcoming 1.7 release)

The command-line interface is simple to use and intuitive. The following, will, for example, create a pass repository, a 20 character password for your LWN account and copy it to the clipboard:

    $ pass init
    $ pass generate -c lwn 20

The main issue with pass is that it doesn't encrypt the name of those entries: if someone were to compromise my machine, they could easily see which sites I have access to simply by listing the passwords stored in ~/.password-store. This is a deliberate design decision by the upstream project, as stated by a mailing list participant, Allan Odgaard:

Using a single file per item has the advantage of shell completion, using version control, browse, move and rename the items in a file browser, edit them in a regular editor (that does GPG, or manually run GPG first), etc.

Odgaard goes on to point out that there are alternatives that do encrypt the entire database (including the site names) if users really need that feature. Furthermore, there is a tomb plugin for pass that encrypts the password store in a LUKS container (called a "tomb"), although it requires explicitly opening and closing the container, which makes it only marginally better than using full disk encryption system-wide. One could also argue that password file names do not hold secret information, only the site name and username, perhaps, and that doesn't require secrecy. I do believe those should be kept secret, however, as they could be used to discover (or prove) which sites you have access to and then used to perform other attacks. One could draw a parallel with the SSH known_hosts file, which used to be plain text but is now hashed so that hosts are more difficult to discover. Also, sharing a database for multi-user support will require some sort of file-sharing mechanism. Given the integrated Git support, this will likely involve setting up a private Git repository for your team, something which may not be accessible to the average Linux user. Nothing keeps you, however, from sharing the ~/.password-store directory through another file sharing mechanism like (say) Syncthing or Dropbox. You can use multiple distinct databases easily using the PASSWORD_STORE_DIR environment variable. For example, you could have a shell alias to use a different repository for your work passwords with:

    alias work-pass="PASSWORD_STORE_DIR=~/work-passwords pass"

Group support comes from a clever use of the GnuPG multiple-recipient encryption support. You simply have to specify multiple OpenPGP identities when initializing the repository, which also works in subdirectories:

    $ pass init -p Ateam me@example.com joelle@example.com
    mkdir: created directory '/home/me/.password-store/Ateam'
    Password store initialized for me@example.com, joelle@example.com
    [master 0e3dbe7] Set GPG id to me@example.com, joelle@example.com.
     1 file changed, 2 insertions(+)
     create mode 100644 Ateam/.gpg-id

The above will configure pass to encrypt the passwords in the Ateam directory for me@example.com and joelle@example.com. Pass depends on GnuPG to do the right thing when encrypting files and how those identities are treated is entirely delegated to GnuPG's default configuration. This could lead to problems if arbitrary keys can be injected into your key ring, which could confuse GnuPG. I would therefore recommend using full key fingerprints instead of user identifiers. Regarding the actual encryption algorithms used, in my tests, GnuPG 1.4.18 and 2.1.18 seemed to default to 256-bit AES for encryption, but that has not always been the case. The chosen encryption algorithm actually depends on the recipient's key preferences, which may vary wildly: older keys and versions may use anything from 128-bit AES to CAST5 or Triple DES. To figure out which algorithm GnuPG chose, you may want to try this pipeline:

    $ echo test   gpg -e -r you@example.com   gpg -d -v
    [...]
    gpg: encrypted with 2048-bit RSA key, ID XXXXXXX, created XXXXX
      "You Person You <you@example.com>"
    gpg: AES256 encrypted data
    gpg: original file name=''
    test

As you can see, pass is primarily a command-line application, which may make it less accessible to regular users. The community has produced different graphical interfaces that are either using pass directly or operate on the storage with their own GnuPG integration. I personally use pass in combination with Rofi to get quick access to my passwords, but less savvy users may want to try the QtPass interface, which should be more user-friendly. QtPass doesn't actually depend on pass and can use GnuPG directly to interact with the pass database; it is available for Linux, BSD, OS X, and Windows.

Browser password managers Most users are probably already using a password manager through their web browser's "remember password" functionality. For example, Chromium will ask if you want it to remember passwords and encrypt them with your operating system's facilities. For Windows, this encrypts the passwords with your login password and, for GNOME, it will store the passwords in the gnome-keyring storage. If you synchronize your Chromium settings with your Google account, Chromium will store those passwords on Google's servers, encrypted with a key that is stored in the Google Account itself. So your passwords are then only as safe as your Google account. Note that this was covered here in 2010, although back then Chromium didn't synchronize with the Google cloud or encrypt with the system-level key rings. That facility was only added in 2013. In Firefox, there's an optional, profile-specific master password that unlocks all passwords. In this case, the issue is that browsers are generally always open, so the vault is always unlocked. And this is for users that actually do pick a master password; users are often completely unaware that they should set one. The unlocking mechanism is a typical convenience-security trade-off: either users need to constantly input their master passwords to login or they don't, and the passwords are available in the clear. In this case, Chromium's approach of actually asking users to unlock their vault seems preferable, even though the developers actually refused to implement the feature for years. Overall, I would recommend against using a browser-based password manager. Even if it is not used for critical sites, you will end up with hundreds of such passwords that are vulnerable while the browser is running (in the case of Firefox) or at the whim of Google (in the case of Chromium). Furthermore, the "auto-fill" feature that is often coupled with browser-based password managers is often vulnerable to serious attacks, which is mentioned below. Finally, because browser-based managers generally lack a proper password generator, users may fail to use properly generated passwords, so they can then be easily broken. A password generator has been requested for Firefox, according to this feature request opened in 2007, and there is a password generator in Chrome, but it is disabled by default and hidden in the mysterious chrome://flags URL.

Other notable password managers Another alternative password manager, briefly mentioned in the previous article, is the minimalistic Assword password manager that, despite its questionable name, is also interesting. Its main advantage over pass is that it uses a single encrypted JSON file for storage, and therefore doesn't leak the name of the entries by default. In addition to copy/paste, Assword also supports automatically entering passphrases in fields using the xdo library. Like pass, it uses GnuPG to encrypt passphrases. According to Assword maintainer Daniel Kahn Gillmor in email, the main issue with Assword is "interaction between generated passwords and insane password policies". He gave the example of the Time-Warner Cable registration form that requires, among other things, "letters and numbers, between 8 and 16 characters and not repeat the same characters 3 times in a row". Another well-known password manager is the commercial LastPass service which released a free-software command-line client called lastpass-cli about three years ago. Unfortunately, the server software of the lastpass.com service is still proprietary. And given that LastPass has had at least two serious security breaches since that release, one could legitimately question whether this is a viable solution for storing important secrets. In general, web-based password managers expose a whole new attack surface that is not present in regular password managers. A 2014 study by University of California researchers showed that, out of five password managers studied, every one of them was vulnerable to at least one of the vulnerabilities studied. LastPass was, in particular, vulnerable to a cross-site request forgery (CSRF) attack that allowed an attacker to bypass account authentication and access the encrypted database.

Problems with password managers When you share a password database within a team, how do you remove access to a member of the team? While you can, for example, re-encrypt a pass database with new keys (thereby removing or adding certain accesses) or change the password on a KeePass database, a hostile party could have made a backup of the database before the revocation. Indeed, in the case of pass, older entries are still in the Git history. So access revocation is a problematic issue found with all shared password managers, as it may actually mean going through every password and changing them online. This fundamental problem with shared secrets can be better addressed with a tool like Vault or SFLvault. Those tools aim to provide teams with easy ways to store dynamic tokens like API keys or service passwords and share them not only with other humans, but also make them accessible to machines. The general idea of those projects is to store secrets in a central server and send them directly to relevant services without human intervention. This way, passwords are not actually shared anymore, which is similar in spirit to the approach taken by centralized authentication systems like Kerberos. If you are looking at password management for teams, those projects may be worth a look. Furthermore, some password managers that support auto-typing were found to be vulnerable to HTML injection attacks: if some third-party ad or content is able to successfully hijack the parent DOM content, it masquerades as a form that could fool auto-typing software as demonstrated by this paper that was submitted at USENIX 2014. Fortunately, KeePass was not vulnerable according to the security researchers, but LastPass was, again, vulnerable.

Future of password managers? All of the solutions discussed here assume you have a trusted computer you regularly have access to, which is a usage pattern that seems to be disappearing with a majority of the population. You could consider your phone to be that trusted device, yet a phone can be lost or stolen more easily than a traditional workstation or even a laptop. And while KeePass has Android and iOS ports, those do not resolve the question of how to share the password storage among those devices or how to back them up. Password managers are fundamentally file-based, and the "file" concept seems to be quickly disappearing, faster than we technologists sometimes like to admit. Looking at some relatives' use of computers, I notice it is less about "files" than images, videos, recipes, and various abstract objects that are stored in the "cloud". They do not use local storage so much anymore. In that environment, password managers lose their primary advantage, which is a local, somewhat offline file storage that is not directly accessible to attackers. Therefore certain password managers are specifically designed for the cloud, like LastPass or web browser profile synchronization features, without necessarily addressing the inherent issues with cloud storage and opening up huge privacy and security issues that we absolutely need to address. This is where the "password hasher" design comes in. Also known as "stateless" or "deterministic" password managers, password hashers are emerging as a convenient solution that could possibly replace traditional password managers as users switch from generic computing platforms to cloud-based infrastructure. We will cover password hashers and the major security challenges they pose in a future article.

Note: this article first appeared in the Linux Weekly News.

KeePass: the popular alternative The most commonly used password-manager design pattern is to store passwords in a file that is encrypted and password-protected. The most popular free-software password manager of this kind is probably KeePass. An important feature of KeePass is the ability to auto-type passwords in forms, most notably in web browsers. This feature makes KeePass really easy to use, especially considering it also supports global key bindings to access passwords. KeePass databases are designed for simultaneous access by multiple users, for example, using a shared network drive. KeePass has a graphical interface written in C#, so it uses the Mono framework on Linux. A separate project, called KeePassX is a clean-room implementation written in C++ using the Qt framework. Both support the AES and Twofish encryption algorithms, although KeePass recently added support for the ChaCha20 cipher. AES key derivation is used to generate the actual encryption key for the database, but the latest release of KeePass also added using Argon2, which was the winner of the July 2015 password-hashing competition. Both programs are more or less equivalent, although the original KeePass seem to have more features in general. The KeePassX project has recently been forked into another project now called KeePassXC that implements a set of new features that are present in KeePass but missing from KeePassX like:

• auto-type on Linux, Mac OS, and Windows
• database merging which allows multi-user support
• using the web site's favicon in the interface

So far, the maintainers of KeePassXC seem to be open to re-merging the project "if the original maintainer of KeePassX in the future will be more active and will accept our merge and changes". I can confirm that, at the time of writing, the original KeePassX project now has 79 pending pull requests and only one pull request was merged since the last release, which was 2.0.3 in September 2016. While KeePass and derivatives allow multiple users to access the same database through the merging process, they do not support multi-party access to a single database. This may be a limiting factor for larger organizations, where you may need, for example, a different password set for different technical support team levels. The solution in this case is to use separate databases for each team, with each team using a different shared secret.

Pass: the standard password manager? I am currently using password-store, or pass, as a password manager. It aims to be "the standard Unix password manager". Pass is a GnuPG-based password manager that features a surprising number of features given its small size:

• copy-paste support
• Git integration
• multi-user/group support
• pluggable extensions (in the upcoming 1.7 release)

The command-line interface is simple to use and intuitive. The following, will, for example, create a pass repository, a 20 character password for your LWN account and copy it to the clipboard:

    $ pass init
    $ pass generate -c lwn 20

The main issue with pass is that it doesn't encrypt the name of those entries: if someone were to compromise my machine, they could easily see which sites I have access to simply by listing the passwords stored in ~/.password-store. This is a deliberate design decision by the upstream project, as stated by a mailing list participant, Allan Odgaard:

Using a single file per item has the advantage of shell completion, using version control, browse, move and rename the items in a file browser, edit them in a regular editor (that does GPG, or manually run GPG first), etc.

Odgaard goes on to point out that there are alternatives that do encrypt the entire database (including the site names) if users really need that feature. Furthermore, there is a tomb plugin for pass that encrypts the password store in a LUKS container (called a "tomb"), although it requires explicitly opening and closing the container, which makes it only marginally better than using full disk encryption system-wide. One could also argue that password file names do not hold secret information, only the site name and username, perhaps, and that doesn't require secrecy. I do believe those should be kept secret, however, as they could be used to discover (or prove) which sites you have access to and then used to perform other attacks. One could draw a parallel with the SSH known_hosts file, which used to be plain text but is now hashed so that hosts are more difficult to discover. Also, sharing a database for multi-user support will require some sort of file-sharing mechanism. Given the integrated Git support, this will likely involve setting up a private Git repository for your team, something which may not be accessible to the average Linux user. Nothing keeps you, however, from sharing the ~/.password-store directory through another file sharing mechanism like (say) Syncthing or Dropbox). You can use multiple distinct databases easily using the PASSWORD_STORE_DIR environment variable. For example, you could have a shell alias to use a different repository for your work passwords with:

    alias work-pass="PASSWORD_STORE_DIR=~/work-passwords pass"

Group support comes from a clever use of the GnuPG multiple-recipient encryption support. You simply have to specify multiple OpenPGP identities when initializing the repository, which also works in subdirectories:

    $ pass init -p Ateam me@example.com joelle@example.com
    mkdir: created directory '/home/me/.password-store/Ateam'
    Password store initialized for me@example.com, joelle@example.com
    [master 0e3dbe7] Set GPG id to me@example.com, joelle@example.com.
     1 file changed, 2 insertions(+)
     create mode 100644 Ateam/.gpg-id

The above will configure pass to encrypt the passwords in the Ateam directory for me@example.com and joelle@example.com. Pass depends on GnuPG to do the right thing when encrypting files and how those identities are treated is entirely delegated to GnuPG's default configuration. This could lead to problems if arbitrary keys can be injected into your key ring, which could confuse GnuPG. I would therefore recommend using full key fingerprints instead of user identifiers. Regarding the actual encryption algorithms used, in my tests, GnuPG 1.4.18 and 2.1.18 seemed to default to 256-bit AES for encryption, but that has not always been the case. The chosen encryption algorithm actually depends on the recipient's key preferences, which may vary wildly: older keys and versions may use anything from 128-bit AES to CAST5 or Triple DES. To figure out which algorithm GnuPG chose, you may want to try this pipeline:

    $ echo test   gpg -e -r you@example.com   gpg -d -v
    [...]
    gpg: encrypted with 2048-bit RSA key, ID XXXXXXX, created XXXXX
      "You Person You <you@example.com>"
    gpg: AES256 encrypted data
    gpg: original file name=''
    test

As you can see, pass is primarily a command-line application, which may make it less accessible to regular users. The community has produced different graphical interfaces that are either using pass directly or operate on the storage with their own GnuPG integration. I personally use pass in combination with Rofi to get quick access to my passwords, but less savvy users may want to try the QtPass interface, which should be more user-friendly. QtPass doesn't actually depend on pass and can use GnuPG directly to interact with the pass database; it is available for Linux, BSD, OS X, and Windows.

Browser password managers Most users are probably already using a password manager through their web browser's "remember password" functionality. For example, Chromium will ask if you want it to remember passwords and encrypt them with your operating system's facilities. For Windows, this encrypts the passwords with your login password and, for GNOME, it will store the passwords in the gnome-keyring storage. If you synchronize your Chromium settings with your Google account, Chromium will store those passwords on Google's servers, encrypted with a key that is stored in the Google Account itself. So your passwords are then only as safe as your Google account. Note that this was covered here in 2010, although back then Chromium didn't synchronize with the Google cloud or encrypt with the system-level key rings. That facility was only added in 2013. In Firefox, there's an optional, profile-specific master password that unlocks all passwords. In this case, the issue is that browsers are generally always open, so the vault is always unlocked. And this is for users that actually do pick a master password; users are often completely unaware that they should set one. The unlocking mechanism is a typical convenience-security trade-off: either users need to constantly input their master passwords to login or they don't, and the passwords are available in the clear. In this case, Chromium's approach of actually asking users to unlock their vault seems preferable, even though the developers actually refused to implement the feature for years. Overall, I would recommend against using a browser-based password manager. Even if it is not used for critical sites, you will end up with hundreds of such passwords that are vulnerable while the browser is running (in the case of Firefox) or at the whim of Google (in the case of Chromium). Furthermore, the "auto-fill" feature that is often coupled with browser-based password managers is often vulnerable to serious attacks, which is mentioned below. Finally, because browser-based managers generally lack a proper password generator, users may fail to use properly generated passwords, so they can then be easily broken. A password generator has been requested for Firefox, according to this feature request opened in 2007, and there is a password generator in Chrome, but it is disabled by default and hidden in the mysterious chrome://flags URL.

Other notable password managers Another alternative password manager, briefly mentioned in the previous article, is the minimalistic Assword password manager that, despite its questionable name, is also interesting. Its main advantage over pass is that it uses a single encrypted JSON file for storage, and therefore doesn't leak the name of the entries by default. In addition to copy/paste, Assword also supports automatically entering passphrases in fields using the xdo library. Like pass, it uses GnuPG to encrypt passphrases. According to Assword maintainer Daniel Kahn Gillmor in email, the main issue with Assword is "interaction between generated passwords and insane password policies". He gave the example of the Time-Warner Cable registration form that requires, among other things, "letters and numbers, between 8 and 16 characters and not repeat the same characters 3 times in a row". Another well-known password manager is the commercial LastPass service which released a free-software command-line client called lastpass-cli about three years ago. Unfortunately, the server software of the lastpass.com service is still proprietary. And given that LastPass has had at least two serious security breaches since that release, one could legitimately question whether this is a viable solution for storing important secrets. In general, web-based password managers expose a whole new attack surface that is not present in regular password managers. A 2014 study by University of California researchers showed that, out of five password managers studied, every one of them was vulnerable to at least one of the vulnerabilities studied. LastPass was, in particular, vulnerable to a cross-site request forgery (CSRF) attack that allowed an attacker to bypass account authentication and access the encrypted database.

Problems with password managers When you share a password database within a team, how do you remove access to a member of the team? While you can, for example, re-encrypt a pass database with new keys (thereby removing or adding certain accesses) or change the password on a KeePass database, a hostile party could have made a backup of the database before the revocation. Indeed, in the case of pass, older entries are still in the Git history. So access revocation is a problematic issue found with all shared password managers, as it may actually mean going through every password and changing them online. This fundamental problem with shared secrets can be better addressed with a tool like Vault or SFLvault. Those tools aim to provide teams with easy ways to store dynamic tokens like API keys or service passwords and share them not only with other humans, but also make them accessible to machines. The general idea of those projects is to store secrets in a central server and send them directly to relevant services without human intervention. This way, passwords are not actually shared anymore, which is similar in spirit to the approach taken by centralized authentication systems like Kerberos). If you are looking at password management for teams, those projects may be worth a look. Furthermore, some password managers that support auto-typing were found to be vulnerable to HTML injection attacks: if some third-party ad or content is able to successfully hijack the parent DOM content, it masquerades as a form that could fool auto-typing software as demonstrated by this paper that was submitted at USENIX 2014. Fortunately, KeePass was not vulnerable according to the security researchers, but LastPass was, again, vulnerable.

Future of password managers? All of the solutions discussed here assume you have a trusted computer you regularly have access to, which is a usage pattern that seems to be disappearing with a majority of the population. You could consider your phone to be that trusted device, yet a phone can be lost or stolen more easily than a traditional workstation or even a laptop. And while KeePass has Android and iOS ports, those do not resolve the question of how to share the password storage among those devices or how to back them up. Password managers are fundamentally file-based, and the "file" concept seems to be quickly disappearing, faster than we technologists sometimes like to admit. Looking at some relatives' use of computers, I notice it is less about "files" than images, videos, recipes, and various abstract objects that are stored in the "cloud". They do not use local storage so much anymore. In that environment, password managers lose their primary advantage, which is a local, somewhat offline file storage that is not directly accessible to attackers. Therefore certain password managers are specifically designed for the cloud, like LastPass or web browser profile synchronization features, without necessarily addressing the inherent issues with cloud storage and opening up huge privacy and security issues that we absolutely need to address. This is where the "password hasher" design comes in. Also known as "stateless" or "deterministic" password managers, password hashers are emerging as a convenient solution that could possibly replace traditional password managers as users switch from generic computing platforms to cloud-based infrastructure. We will cover password hashers and the major security challenges they pose in a future article.

Note: this article first appeared in the Linux Weekly News.

• If you have a technically competent host, your data is backed up regularly and the database is available nearly 100% of the time
• If you have a politically trust-worthy host, your host will notify you and put up a fight before turning any of your data over to a government agent
• If you drop your phone in the toilet you can always login from another computer to access your data
• If you save your password in your browser and your laptop is stolen, you can always change your password to prevent the thief from accessing your data
• You can easily share your data with others by creating new usernames and passwords

• If your host is not technically competent or polically trust-worthy, you could lose all of your data to a hard drive crash or subpoena
• Even if your host is competent, all of your data is one previously undiscovered vulnerability away from being hacked
• Even if your host is politically trust-worthy, you cannot always stop a subpoena, particularly given the legal escalations of tools like national security letters

• Availability: if you lose your device, you would need to restore from backup - which is much more difficult than simply logging in from another device
• Collaboration: you simply can't share this data with anyone else

from apt.cache import Cache
mycache = Cache()
mycache.update()                   # apt-get update
mycache.open()                     # re-open
mycache.upgrade(dist_upgrade=True) # apt-get dist-upgrade
mycache.commit()                   # apply

boil out selections As widely known, there is a feature of dpkg which helps to move a package inventory from one installation to another by just using a text file with a list of installed packages. A selections list containing all installed package could be easily generated with $ dpkg --get-selections > selections.txt. The resulting file then looks something similar like this:

$ cat selections.txt
0ad                                 install
0ad-data                            install
0ad-data-common                     install
a2ps                                install
abi-compliance-checker              install
abi-dumper                          install
abigail-tools                       install
accountsservice                     install
acl                                 install
acpi                                install

The counterpart for this operation (--set-selections) could be used to reinstall (add) the complete package inventory on another installation resp. computer (that needs superuser rights), like that s explained in the manpage dpkg(1). No problem so far. The problem is, if that list contains a package which couldn t be found in any of the package inventories which are set up in /etc/apt/sources.list(.d/) on the target system, dpkg stops the whole process:

# dpkg --set-selections < selections.txt
dpkg: warning: package not in database at line 524: google-chrome-beta
dpkg: warning: found unknown packages; this might mean the available database
is outdated, and needs to be updated through a frontend method

Thus, manually downloaded and installed wild packages from unofficial package sources are problematic for this approach, because the package installer simply doesn t know where to get them. Luckily, dpkg puts out the relevant package names, but instead of having them removed manually with an editor this little Python script for python3-apt automatically deletes any of these packages from a selections file:

#!/usr/bin/env python3
import sys
import apt_pkg
apt_pkg.init()
cache = apt_pkg.Cache()
infile = open(sys.argv[1])
outfile_name = sys.argv[1] + '.boiled'
outfile = open(outfile_name, "w")
for line in infile:
    package = line.split()[0]
    if package in cache:
        outfile.write(line)
infile.close()
outfile.close()
sys.exit(0)

The script takes one argument which is the name of the selections file which has been generated by dpkg. The low level module apt_pkg first has to been initialized with apt_pkg.init(). Then apt_pkg.Cache() can be used to instantiate a cache object (here: cache). That object is iterable, thus it s easy to not perform something if a package from that list couldn t be found in the database, like not copying the corresponding line into the outfile (.boiled), while the others are copied. The result then looks something like this:

$ diff selections.txt selections.txt.boiled 
3780d3779
< python-timemachine   install
4438d4436
< wlan-supercracker    install

That script might be useful also for moving from one distribution resp. derivative to another (like from Ubuntu to Debian). For productive use, open() should be of course secured against FileNotFound and IOError-s to prevent program crashs on such events.

purge rc-s Like also widely known, deinstalled packages leave stuff like configuration files, maintainer scripts and logs on the computer, to save that if the package gets reinstalled at some point in the future. That happens if dpkg has been used with -r/--remove instead of -P/--purge, which also removes these files which are left otherwise. These packages are then marked as rc in the package archive, like:

$ dpkg -l   grep ^rc
rc  firebird2.5-common          2.5.6.27020.ds4-3   amd64   common files for firebird 2.5 servers and clients
rc  firebird2.5-server-common   2.5.6.27020.ds4-3   amd64   common files for firebird 2.5 servers
rc  firebird3.0-common          3.0.1.32609.ds4-8   all     common files for firebird 3.0 server, client and utilities
rc  imagemagick-common          8:6.9.6.2+dfsg-2    all     image manipulation programs -- infrastructure dummy package

It could be purged over them afterwards to completely remove them from the system. There are several shell coding snippets to be found on the net for completing this job automatically, like this one here:

dpkg -l   grep "^rc"   sed  e "s/^rc //"  e "s/ .*$//"   \
xargs dpkg  purge

The first thing which is needed to handle this by a Python script is the information that in apt_pkg, the package state rc per default is represented by the code 5:

>>> testpackage = cache['firebird2.5-common']
>>> testpackage.current_state
5

For changing things in the database apt_pkg.DepCache() could be docked onto an cache object to manipulate the installation state of a package within, like marking it to be removed resp. purged:

>>> mydepcache = apt_pkg.DepCache(mycache)
>>> mydepcache.mark_delete(testpackage, True) # True = purge
>>> mydepcache.marked_delete(testpackage)
True

That s basically all which is needed for an old package purging maintenance script in Python 3, another iterator as package filter and there you go:

#!/usr/bin/env python3
import sys
import apt_pkg
from apt.progress.text import AcquireProgress
from apt.progress.base import InstallProgress
acquire = AcquireProgress()
install = InstallProgress()
apt_pkg.init()
cache = apt_pkg.Cache()
depcache = apt_pkg.DepCache(cache)
for paket in cache.packages:
    if paket.current_state == 5:
        depcache.mark_delete(paket, True)
depcache.commit(acquire, install)

The method DepCache.commit() applies the changes to the package archive at the end, and it needs apt_progress to perform. Of course this script needs superuser rights to run. It then returns something like this:

$ sudo ./rc-purge 
Reading package lists... Done
Building dependency tree
Reading state information... Done
Fetched 0 B in 0s (0 B/s)
custom fork found
got pid: 17984
got pid: 0
got fd: 4
(Reading database ... 701434 files and directories currently installed.)
Purging configuration files for libmimic0:amd64 (1.0.4-2.3) ...
Purging configuration files for libadns1 (1.5.0~rc1-1) ...
Purging configuration files for libreoffice-sdbc-firebird (1:5.2.2~rc2-2) ...
Purging configuration files for vlc-nox (2.2.4-7) ...
Purging configuration files for librlog5v5 (1.4-4) ...
Purging configuration files for firebird3.0-common (3.0.1.32609.ds4-8) ...
Purging configuration files for imagemagick-common (8:6.9.6.2+dfsg-2) ...
Purging configuration files for firebird2.5-server-common (2.5.6.27020.ds4-3)

It s not yet production ready (like there s an infinite loop if dpkg returns error code 1 like from can t remove non empty folder ). But generally, ATTENTION: be very careful with typos and other mistakes if you want to use that code snippet, a false script performing changes on the package database might destroy the integrity of your system, and you don t want that to happen.

detect wild packages Like said above, installed Debian packages might be called wild if they have been downloaded from somewhere on the net and installed manually, like that is done from time to time on many systems. If you want to remove that whole class of packages again for any reason, the question would be how to detect them. A characteristic element is that there is no source connected to such a package, and that could be detected by Python scripting using again the bindings for the APT libraries. The package object doesn t have an associated method to query its source, because the origin is always connected to a specific package version, like some specific version might have come from security updates for example. The current version of a package can be queried with DepCache.get_candidate_ver() which returns a complex apt_pkg.Version object:

>>> import apt_pkg
>>> apt_pkg.init()
>>> mycache = apt_pkg.Cache()
Reading package lists... Done
Building dependency tree
Reading state information... Done
>>> mydepcache = apt_pkg.DepCache(mycache)
>>> testpackage = mydepcache.get_candidate_ver(mycache['nano'])
>>> testpackage
<apt_pkg.Version object: Pkg:'nano' Ver:'2.7.4-1' Section:'editors'  Arch:'amd64' Size:484790 ISize:2092032 Hash:33578 ID:31706 Priority:2>

For version objects there is the method file_list available, which returns a list containing PackageFile() objects:

>>> testpackage.file_list
[(<apt_pkg.PackageFile object: filename:'/var/lib/apt/lists/httpredir.debian.org_debian_dists_testing_main_binary-amd64_Packages'  a=testing,c=main,v=,o=Debian,l=Debian arch='amd64' site='httpredir.debian.org' IndexType='Debian Package Index' Size=38943764 ID:0>, 669901L)]

These file objects contain the index files which are associated with a specific package source (a downloaded package index), which could be read out easily (using a for-loop because there could be multiple file objects):

>>> for files in testpackage.file_list:
...     print(files[0].filename)
/var/lib/apt/lists/httpredir.debian.org_debian_dists_testing_main_binary-amd64_Packages

That explains itself: the nano binary package on this amd64 computer comes from httpredir.debian.org/debian testing main. If a package is wild that means it was installed manually, so there is no associated index file to be found, but only /var/lib/dpkg/status (libcudnn5 is not in the official package archives but distributed by Nvidia as a .deb package):

>>> testpackage2 = mydepcache.get_candidate_ver(mycache['libcudnn5'])
>>> for files in testpackage2.file_list:
...     print(files[0].filename)
/var/lib/dpkg/status

The simple trick now is to find all packages which have only /var/lib/dpkg/status as associated system file (that doesn t refer to what packages contain), an not an index file representing a package source. There s a little pitfall: that s truth also for virtual packages. But virtual packages commonly don t have an associated version (python-apt docs: to check whether a package is virtual; that is, it has no versions and is provided at least once ), and that can be queried by Package.has_versions. A filter to find out any packages that aren t virtual packages, are solely associated to one system file, and that file is /var/lib/dpkg/status, then goes like this:

for package in cache.packages:
    if package.has_versions:
        version = mydepcache.get_candidate_ver(package)
        if len(version.file_list) == 1:
            if 'dpkg/status' in version.file_list[0][0].filename:
                print(package.name)

On my Debian testing system this puts out a quite interesting list. It lists all the wild packages like libcudnn5, but also packages which are recently not in testing because they have been temporarily removed by AUTORM due to release critical bugs. Then there s all the obsolete stuff which have been installed from the package archives once and then being forgotten like old kernel header packages ( obsolete packages in dselect). So this snippet brings up other stuff, too. Thus, this might be more experimental stuff so far, though.

Developer time

Arguably the greatest resource of a project is the time its developers can devote to it. Unless it is a very large, well supported project like the Kernel or libreoffice almost all developer time is voluntary.

Developer focus

Any given developer is likely to work on an area of code that interests them in preference to one that does not. This means if a developer must do work which does not interest them they may loose focus and not work on the project at all.

Developer skillset

A given developer may not have the skillset necessary to work on a feature, this is especially acute when considering minority platforms which often have very, very few skilled developers available.

Developer access

It should be obvious that software that only requires commodity hardware and software to develop is much cheaper than that which requires special hardware and software. To use our earlier example the cocoa frontend required an apple computer running MAC OS X to compile and test, this resource was very limited and the project only had access to two such systems via remote desktop. These systems also had to serve as CI builders and required physical system administration as they could not be virtualized.

Support

Once a project releases useful software it generally gains users outside of the developers. Supporting users consumes developer time and generally causes them to focus on things other than code that interests them.

While most developers have enough pride in what they produce to fix bugs, users must always remember that the main freedom they get from OSS is they recived the code and can change it themselves, there is no requirement for a developer to do anything for them.

Resources

A project requires a website, code repository, wiki, CI systems etc. which must all be paid for. Netsurf for example is fortunate to have Pepperfish look after our website hosting at favorable rates, Mythic beasts provide exceptionally good rates for the CI system virtual machine along with hardware donations (our apple macs were donated by them) and Collabora for providing physical hosting for our virtual machine server.

Despite these incredibly good deals the project still spends around 200gbp (250usd) a year on overheads, these services obviously benefit the whole project including minority platforms but are generally donated by users of the more popular platforms.

Developer learning

A developer may implement a feature to allow them to learn a new technology or skill

Project diversity

A feature may mean the project gets built in a new environment which reveals issues or opportunities in unconnected code. For example the Debian OS is built on a variety of hardware platforms and sometimes reveals issues in software by compiling it on big endian systems. These issues are often underlying bugs that are causing errors which are simply not observed on a little endian platform.

More users

Gaining users of the software is often a benefit and although most OSS developers are contributing for personal reasons having their work appreciated by others is often a factor. This might be seen as the other side of the support cost.

Changes in version 0.1.1 (2017-xx-yy)

• Synchronized multiple times with ccptoml upstream adding support for local datetime and local date and more (PR #9, #10, PR #11)
• Dates are now first class types, some support for local versus UTC times was added (though it may be adviseable to stick with UTC)
• Parsing from (R) character variables is now supported as well
• Output from print.toml no longer prints extra newlines

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. Please report excessive re-aggregation in third-party for-profit settings.

• another hobby? check!
• new gear to learn? check!
• something more palpable to do with my photos? good enough reason, check!

• first question: glossy or matte ink?
• if glossy, which type of paper? actually glossy (uh, no), semi-gloss, pearl, satin?
• if matte, are we talking about textured or smooth matte?
• what weight? fine art paper that I tested can go from a very interesting 100gsm (almost like standard paper) Rice Paper, to 210, 286, 310 (quite standard), 325, 350 and finally towards 390-410 heavy canvas;
• on the more professional side, do you care about lifetime of paper? if you choose yes, then take care of choosing paper with no OBA optical brightening agents;
• and if you really want to go deep, what base? cellulose, alpha-cellulose or cotton?

1. People who directly launch our image and treat it like a classic VPS. These users most likely will be logging into their instances via ssh and configuring it interactively, though they may also install and use a configuration management system at some point.
2. People who directly launch our images but configure them automatically via launch-time configuration passed to the cloud-init process on the agent. This automatic configuration may optionally serve to bootstrap the instance into a more complete configuration management system. The user may or may not ever actually log in to the system at all.
3. People who will not use our images directly at all, but will instead construct their own image based on ours. They may do this by launching an instance of our image, customizing it, and snapshotting it, or they may build a custom image from scratch by reusing and modifying the tools and configuration that we use to generate our images.

sudo fai-diskimage --hostname stretch-image --size 8G \
--class DEBIAN,STRETCH,AMD64,GRUB_PC,DEVEL,CLOUD,EC2 \
/tmp/stretch-image.raw

PACKAGES install
apache2

sudo fai-diskimage --hostname stretch-image --size 8G \
--class DEBIAN,STRETCH,AMD64,GRUB_PC,DEVEL,CLOUD,EC2,HTTPD \
/tmp/stretch-image.raw

admin@ip-10-0-0-64:~$ sudo partx --show /tmp/stretch-image.raw
NR START      END  SECTORS SIZE NAME UUID
 1  2048 16777215 16775168   8G      ed093314-01
admin@ip-10-0-0-64:~$ sudo partx -a /tmp/stretch-image.raw 
partx: /dev/loop0: error adding partition 1
admin@ip-10-0-0-64:~$ lsblk 
NAME      MAJ:MIN RM    SIZE RO TYPE MOUNTPOINT
xvda      202:0    0      8G  0 disk 
 xvda1   202:1    0 1007.5K  0 part 
 xvda2   202:2    0      8G  0 part /
loop0       7:0    0      8G  0 loop 
 loop0p1 259:0    0      8G  0 loop 
admin@ip-10-0-0-64:~$ sudo mount /dev/loop0p1 /mnt/
admin@ip-10-0-0-64:~$ ls /mnt/
bin/   dev/  home/        initrd.img.old@  lib64/       media/  opt/   root/  sbin/  sys/  usr/  vmlinuz@
boot/  etc/  initrd.img@  lib/             lost+found/  mnt/    proc/  run/   srv/   tmp/  var/  vmlinuz.old@

1. Attach a secondary EBS volume to your EC2 instance. It must be large enough to hold the raw disk image you created.
2. Use dd to write your image to the secondary volume, e.g. sudo dd if=/tmp/stretch-image.raw of=/dev/xvdb
3. Use the volume-to-ami.sh script in the fail-cloud-image repo to snapshot the volume and register the resulting snapshot with AWS as a new AMI. Example: ./volume-to-ami.sh vol-04351c30c46d7dd6e

R> library(anytime)
R> anytime("Thu Sep 01 10:11:12 CDT 2016")
[1] "2016-09-01 10:11:12 CDT"
R> anytime("Thu Sep 01 10:11:12.123456 CDT 2016") # with frac. seconds
[1] "2016-09-01 10:11:12.123456 CDT"
R> 

Changes in anytime version 0.2.1 (2017-02-09)

• The new DatetimeVector class from Rcpp is now used, and proper versioned Depends: have been added (#43)
• The anydate and utcdate functions convert again from factor and ordered (#46 closing #44)
• A format similar to RFC 28122 but with additonal timezone text can now be parsed (#48 closing #47)
• Conversion from POSIXt to Date now also respect the timezone (#50 closing #49)
• The internal .onLoad functions was updated
• The Travis setup uses https to fetch the run script

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. Please report excessive re-aggregation in third-party for-profit settings.

package main
import (
    "log"
    "net"
    "net/http"
)
func main()  
    l, err := net.Listen("tcp", ":8081")
    if err != nil  
        log.Panicf("cannot listen: %s", err)
     
    http.Serve(l, nil)
 

[Unit]
Description=404 micro-service
[Service]
Type=notify
ExecStart=/usr/bin/404
WatchdogSec=30s
Restart=on-failure
[Install]
WantedBy=multi-user.target

Readiness The classic way for an Unix daemon to signal its readiness is to daemonize. Technically, this is done by calling fork(2) twice (which also serves other intents). This is a very common task and the BSD systems, as well as some other C libraries, supply a daemon(3) function for this purpose. Services are expected to daemonize only when they are ready (after reading configuration files and setting up a listening socket, for example). Then, a system can reliably initialize its services with a simple linear script:

syslogd
unbound
ntpd -s

Each daemon can rely on the previous one being ready to do its work. The sequence of actions is the following:

1. syslogd reads its configuration, activates /dev/log, daemonizes.
2. unbound reads its configuration, listens on 127.0.0.1:53, daemonizes.
3. ntpd reads its configuration, connects to NTP peers, waits for clock to be synchronized², daemonizes.

With systemd, we would use Type=fork in the service file. However, Go s runtime does not support that. Instead, we use Type=notify. In this case, systemd expects the daemon to signal its readiness with a message to an Unix socket. go-systemd package handles the details for us:

package main
import (
    "log"
    "net"
    "net/http"
    "github.com/coreos/go-systemd/daemon"
)
func main()  
    l, err := net.Listen("tcp", ":8081")
    if err != nil  
        log.Panicf("cannot listen: %s", err)
     
    daemon.SdNotify(false, "READY=1") //  
    http.Serve(l, nil)                //  
 

It s important to place the notification after net.Listen() (in ): if the notification was sent earlier, a client would get connection refused when trying to use the service. When a daemon listens to a socket, connections are queued by the kernel until the daemon is able to accept them (in ). If the service is not run through systemd, the added line is a no-op.

Liveness Another interesting feature of systemd is to watch the service and restart it if it happens to crash (thanks to the Restart=on-failure directive). It s also possible to use a watchdog: the service sends watchdog keep-alives at regular interval. If it fails to do so, systemd will restart it. We could insert the following code just before http.Serve() call:

go func()  
    interval, err := daemon.SdWatchdogEnabled(false)
    if err != nil   interval == 0  
        return
     
    for  
        daemon.SdNotify(false, "WATCHDOG=1")
        time.Sleep(interval / 3)
     
 ()

However, this doesn t add much value: the goroutine is unrelated to the core business of the service. If for some reason, the HTTP part gets stuck, the goroutine will happily continue to send keep-alives to systemd. In our example, we can just do a HTTP query before sending the keep-alive. The internal loop can be replaced with this code:

for  
    _, err := http.Get("http://127.0.0.1:8081") //  
    if err == nil  
        daemon.SdNotify(false, "WATCHDOG=1")
     
    time.Sleep(interval / 3)
 

In , we connect to the service to check if it s still working. If we get some kind of answer, we send a watchdog keep-alive. If the service is unavailable or if http.Get() gets stuck, systemd will trigger a restart. There is no universal recipe. However, checks can be split into two groups:

• Before sending a keep-alive, you execute an active check on the components of your service. The keep-alive is sent only if all checks are successful. The checks can be internal (like in the above example) or external (for example, check with a query to the database).
• Each component reports its status, telling if it s alive or not. Before sending a keep-alive, you check the reported status of all components (passive check). If some components are late or reported fatal errors, don t send the keep-alive.

If possible, recovery from errors (for example, with a backoff retry) and self-healing (for example, by reestablishing a network connection) is always better, but the watchdog is a good tool to handle the worst cases and avoid too complex recovery logic. For example, if a component doesn t know how to recover from an exceptional condition³, instead of using panic(), it could signal its situation before dying. Another dedicated component could try to resolve the situation by restarting the faulty component. If it fails to reach an healthy state in time, the watchdog timer will trigger and the whole service will be restarted.

---

1. Depending on the distribution, this should be installed in /lib/systemd/system or /usr/lib/systemd/system. Check with the output of the command pkg-config systemd --variable=systemdsystemunitdir.
2. This highly depends on the NTP daemon used. OpenNTPD doesn t wait unless you use the -s option. ISC NTP doesn t either unless you use the --wait-sync option.
3. An example of an exceptional condition is to reach the limit on the number of file descriptors. Self-healing from this situation is difficult and it s easy to get stuck in a loop.

• Vim and Emacs (for which I use the debian package elpa-solarized-theme).
• Midnight Commander, for which I currently use peel's theme, although I'm not happy with it; interestingly, the default theme almost works on 16-custom-colours light terminal scheme, but not quite on the dark one.
• Mutt, which is both in the main combined repository but also on the separate one. I'm not really happy with mutt's theme either, but that seems mostly because I was using a quite different theme before. I'll try to improve what I feel is missing over time.
• dircolors; I found this to be an absolute requirement for good readability of ls --color, as the defaults are too bad
• I also took the opportunity to unify my git diff and colordiff theme, but this was not really something that I found and took 'as-is' from some repository; I basically built my own theme.

• by changing the Xresources/terminal 16 basic colours to custom RGB values, or:
• by using approximations from the fixed 256 colours available in the xterm-256color terminfo

• using customised 16-colour means that all terminal programs get the new colours scheme, even if they were designed (colour-wise) based on the standard values; this makes some things pretty unreadable (hence the need to fix dircolors), but at least somewhat consistent.
• using 256-colour palette, unchanged programs stay the same, but now they look very different than the programs that were updated to solarized; note thought I haven't tested this, but that's how I understand things would be.

What makes a good password? A "good password" may mean different things to different people. I will assert that a good password has the following properties:

• high entropy: hard to guess for machines
• transferable: easy to communicate for humans or transfer across various protocols for computers
• memorable: easy to remember for humans

High entropy means that the password should be unpredictable to an attacker, for all practical purposes. It is tempting (and not uncommon) to choose a password based on something else that you know, but unfortunately those choices are likely to be guessable, no matter how "secret" you believe it is. Yes, with enough effort, an attacker can figure out your birthday, the name of your first lover, your mother's maiden name, where you were last summer, or other secrets people think they have. The only solution here is to use a password randomly generated with enough randomness or "entropy" that brute-forcing the password will be practically infeasible. Considering that a modern off-the-shelf graphics card can guess millions of passwords per second using freely available software like hashcat, the typical requirement of "8 characters" is not considered enough anymore. With proper hardware, a powerful rig can crack such passwords offline within about a day. Even though a recent US National Institute of Standards and Technology (NIST) draft still recommends a minimum of eight characters, we now more often hear recommendations of twelve characters or fourteen characters. A password should also be easily "transferable". Some characters, like & or !, have special meaning on the web or the shell and can wreak havoc when transferred. Certain software also has policies of refusing (or requiring!) some special characters exactly for that reason. Weird characters also make it harder for humans to communicate passwords across voice channels or different cultural backgrounds. In a more extreme example, the popular Signal software even resorted to using only digits to transfer key fingerprints. They outlined that numbers are "easy to localize" (as opposed to words, which are language-specific) and "visually distinct". But the critical piece is the "memorable" part: it is trivial to generate a random string of characters, but those passwords are hard for humans to remember. As xkcd noted, "through 20 years of effort, we've successfully trained everyone to use passwords that are hard for human to remember but easy for computers to guess". It explains how a series of words is a better password than a single word with some characters replaced. Obviously, you should not need to remember all passwords. Indeed, you may store some in password managers (which we'll look at in another article) or write them down in your wallet. In those cases, what you need is not a password, but something I would rather call a "token", or, as Debian Developer Daniel Kahn Gillmor (dkg) said in a private email, a "high entropy, compact, and transferable string". Certain APIs are specifically crafted to use tokens. OAuth, for example, generates "access tokens" that are random strings that give access to services. But in our discussion, we'll use the term "token" in a broader sense. Notice how we removed the "memorable" property and added the "compact" one: we want to efficiently convert the most entropy into the shortest password possible, to work around possibly limiting password policies. For example, some bank cards only allow 5-digit security PINs and most web sites have an upper limit in the password length. The "compact" property applies less to "passwords" than tokens, because I assume that you will only use a password in select places: your password manager, SSH and OpenPGP keys, your computer login, and encryption keys. Everything else should be in a password manager. Those tools are generally under your control and should allow large enough passwords that the compact property is not particularly important.

Generating secure passwords We'll look now at how to generate a strong, transferable, and memorable password. These are most likely the passwords you will deal with most of the time, as security tokens used in other settings should actually never show up on screen: they should be copy-pasted or automatically typed in forms. The password generators described here are all operated from the command line. Password managers often have embedded password generators, but usually don't provide an easy way to generate a password for the vault itself. The previously mentioned xkcd cartoon is probably a common cultural reference in the security crowd and I often use it to explain how to choose a good passphrase. It turns out that someone actually implemented xkcd author Randall Munroe's suggestion into a program called xkcdpass:

    $ xkcdpass
    estop mixing edelweiss conduct rejoin flexitime

In verbose mode, it will show the actual entropy of the generated passphrase:

    $ xkcdpass -V
    The supplied word list is located at /usr/lib/python3/dist-packages/xkcdpass/static/default.txt.
    Your word list contains 38271 words, or 2^15.22 words.
    A 6 word password from this list will have roughly 91 (15.22 * 6) bits of entropy,
    assuming truly random word selection.
    estop mixing edelweiss conduct rejoin flexitime

Note that the above password has 91 bits of entropy, which is about what a fifteen-character password would have, if chosen at random from uppercase, lowercase, digits, and ten symbols:

    log2((26 + 26 + 10 + 10)^15) = approx. 92.548875

It's also interesting to note that this is closer to the entropy of a fifteen-letter base64 encoded password: since each character is six bits, you end up with 90 bits of entropy. xkcdpass is scriptable and easy to use. You can also customize the word list, separators, and so on with different command-line options. By default, xkcdpass uses the 2 of 12 word list from 12 dicts, which is not specifically geared toward password generation but has been curated for "common words" and words of different sizes. Another option is the diceware system. Diceware works by having a word list in which you look up words based on dice rolls. For example, rolling the five dice "1 4 2 1 4" would give the word "bilge". By rolling those dice five times, you generate a five word password that is both memorable and random. Since paper and dice do not seem to be popular anymore, someone wrote that as an actual program, aptly called diceware. It works in a similar fashion, except that passwords are not space separated by default:

    $ diceware
    AbateStripDummy16thThanBrock

Diceware can obviously change the output to look similar to xkcdpass, but can also accept actual dice rolls for those who do not trust their computer's entropy source:

    $ diceware -d ' ' -r realdice -w en_orig
    Please roll 5 dice (or a single dice 5 times).
    What number shows dice number 1? 4
    What number shows dice number 2? 2
    What number shows dice number 3? 6
    [...]
    Aspire O's Ester Court Born Pk

The diceware software ships with a few word lists, and the default list has been deliberately created for generating passwords. It is derived from the standard diceware list with additions from the SecureDrop project. Diceware ships with the EFF word list that has words chosen for better recognition, but it is not enabled by default, even though diceware recommends using it when generating passwords with dice. That is because the EFF list was added later on. The project is currently considering making the EFF list be the default. One disadvantage of diceware is that it doesn't actually show how much entropy the generated password has those interested need to compute it for themselves. The actual number depends on the word list: the default word list has 13 bits of entropy per word (since it is exactly 8192 words long), which means the default 6 word passwords have 78 bits of entropy:

    log2(8192) * 6 = 78

Both of these programs are rather new, having, for example, entered Debian only after the last stable release, so they may not be directly available for your distribution. The manual diceware method, of course, only needs a set of dice and a word list, so that is much more portable, and both the diceware and xkcdpass programs can be installed through pip. However, if this is all too complicated, you can take a look at Openwall's passwdqc, which is older and more widely available. It generates more memorable passphrases while at the same time allowing for better control over the level of entropy:

    $ pwqgen
    vest5Lyric8wake
    $ pwqgen random=78
    Theme9accord=milan8ninety9few

For some reason, passwdqc restricts the entropy of passwords between the bounds of 24 and 85 bits. That tool is also much less customizable than the other two: what you see here is pretty much what you get. The 4096-word list is also hardcoded in the C source code; it comes from a Usenet sci.crypt posting from 1997. A key feature of xkcdpass and diceware is that you can craft your own word list, which can make dictionary-based attacks harder. Indeed, with such word-based password generators, the only viable way to crack those passwords is to use dictionary attacks, because the password is so long that character-based exhaustive searches are not workable, since they would take centuries to complete. Changing from the default dictionary therefore brings some advantage against attackers. This may be yet another "security through obscurity" procedure, however: a naive approach may be to use a dictionary localized to your native language (for example, in my case, French), but that would deter only an attacker that doesn't do basic research about you, so that advantage is quickly lost to determined attackers. One should also note that the entropy of the password doesn't depend on which word list is chosen, only its length. Furthermore, a larger dictionary only expands the search space logarithmically; in other words, doubling the word-list length only adds a single bit of entropy. It is actually much better to add a word to your password than words to the word list that generates it.

Generating security tokens As mentioned before, most password managers feature a way to generate strong security tokens, with different policies (symbols or not, length, etc). In general, you should use your password manager's password-generation functionality to generate tokens for sites you visit. But how are those functionalities implemented and what can you do if your password manager (for example, Firefox's master password feature) does not actually generate passwords for you? pass, the standard UNIX password manager, delegates this task to the widely known pwgen program. It turns out that pwgen has a pretty bad track record for security issues, especially in the default "phoneme" mode, which generates non-uniformly distributed passwords. While pass uses the more "secure" -s mode, I figured it was worth removing that option to discourage the use of pwgen in the default mode. I made a trivial patch to pass so that it generates passwords correctly on its own. The gory details are in this email. It turns out that there are lots of ways to skin this particular cat. I was suggesting the following pipeline to generate the password:

    head -c $entropy /dev/random   base64   tr -d '\n='

The above command reads a certain number of bytes from the kernel (head -c $entropy /dev/random) encodes that using the base64 algorithm and strips out the trailing equal sign and newlines (for large passwords). This is what Gillmor described as a "high-entropy compact printable/transferable string". The priority, in this case, is to have a token that is as compact as possible with the given entropy, while at the same time using a character set that should cause as little trouble as possible on sites that restrict the characters you can use. Gillmor is a co-maintainer of the Assword password manager, which chose base64 because it is widely available and understood and only takes up 33% more space than the original 8-bit binary encoding. After a lengthy discussion, the pass maintainer, Jason A. Donenfeld, chose the following pipeline:

    read -r -n $length pass < <(LC_ALL=C tr -dc "$characters" < /dev/urandom)

The above is similar, except it uses tr to directly to read characters from the kernel, and selects a certain set of characters ($characters) that is defined earlier as consisting of [:alnum:] for letters and digits and [:graph:] for symbols, depending on the user's configuration. Then the read command extracts the chosen number of characters from the output and stores the result in the pass variable. A participant on the mailing list, Brian Candler, has argued that this wastes entropy as the use of tr discards bits from /dev/urandom with little gain in entropy when compared to base64. But in the end, the maintainer argued that reading "reading from /dev/urandom has no [effect] on /proc/sys/kernel/random/entropy_avail on Linux" and dismissed the objection. Another password manager, KeePass uses its own routines to generate tokens, but the procedure is the same: read from the kernel's entropy source (and user-generated sources in case of KeePass) and transform that data into a transferable string.

Conclusion While there are many aspects to password management, we have focused on different techniques for users and developers to generate secure but also usable passwords. Generating a strong yet memorable password is not a trivial problem as the security vulnerabilities of the pwgen software showed. Furthermore, left to their own devices, users will generate passwords that can be easily guessed by a skilled attacker, especially if they can profile the user. It is therefore essential we provide easy tools for users to generate strong passwords and encourage them to store secure tokens in password managers.

Note: this article first appeared in the Linux Weekly News.

• Header: this one contains basic information such as the virtual size of the image, the version number, and pointers to where the rest of the metadata is located, among other things.
• Data clusters: the data that the virtual machine sees.
• L1 and L2 tables: a two-level structure that maps the virtual disk that the guest can see to the actual location of the data clusters in the qcow2 file.
• Refcount table and blocks: a two-level structure with a reference count for each data cluster. Internal snapshots use this: a cluster with a reference count >= 2 means that it s used by other snapshots, and therefore any modifications require a copy-on-write operation.

1. Checks that run in constant time. These are equally fast for all kinds of images and I don t think they re worth disabling.
   • main-header
   • active-l1
   • refcount-table
   • snapshot-table
2. Checks that run in variable time but don t need to read anything from disk.
   • refcount-block
   • active-l2
   • inactive-l1
3. Checks that need to read data from disk. There is just one check here and it s only needed if there are internal snapshots.
   • inactive-l2

• inactive-l1: This is a variable length check because it depends on the number of internal snapshots in the qcow2 image. However its performance impact is likely to be negligible in all cases so I don t think it s worth bothering with.
• active-l2: This check depends on the virtual size of the image, and on the percentage that has already been allocated. This check might have some impact if the image is very large (several hundred GBs or more). In that case one way to deal with it is to create an image with a larger cluster size. This also has the nice side effect of reducing the amount of memory needed for the L2 cache.
• refcount-block: This check depends on the actual size of the qcow2 file and it s independent from its virtual size. This check is relatively expensive even for small images, so if you notice performance problems chances are that they are due to this one. The good news is that we have been working on optimizing it, so if it s slowing down your VMs the problem might go away completely in QEMU 2.9.

A simple terminal Let s start small with a terminal with the default settings. We ll write that in C. Another supported option is Vala.

#include <vte/vte.h>
int
main(int argc, char *argv[])
 
    GtkWidget *window, *terminal;
    /* Initialise GTK, the window and the terminal */
    gtk_init(&argc, &argv);
    terminal = vte_terminal_new();
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "myterm");
    /* Start a new shell */
    gchar **envp = g_get_environ();
    gchar **command = (gchar *[]) g_strdup(g_environ_getenv(envp, "SHELL")), NULL  ;
    g_strfreev(envp);
    vte_terminal_spawn_sync(VTE_TERMINAL(terminal),
        VTE_PTY_DEFAULT,
        NULL,       /* working directory  */
        command,    /* command */
        NULL,       /* environment */
        0,          /* spawn flags */
        NULL, NULL, /* child setup */
        NULL,       /* child pid */
        NULL, NULL);
    /* Connect some signals */
    g_signal_connect(window, "delete-event", gtk_main_quit, NULL);
    g_signal_connect(terminal, "child-exited", gtk_main_quit, NULL);
    /* Put widgets together and run the main loop */
    gtk_container_add(GTK_CONTAINER(window), terminal);
    gtk_widget_show_all(window);
    gtk_main();
 

You can compile it with the following command:

gcc -O2 -Wall $(pkg-config --cflags --libs vte-2.91) term.c -o term

And run it with ./term:

More features From here, you can have a look at the documentation to alter behavior or add more features. Here are three examples.

Colors You can define the 16 basic colors with the following code:

#define CLR_R(x)   (((x) & 0xff0000) >> 16)
#define CLR_G(x)   (((x) & 0x00ff00) >>  8)
#define CLR_B(x)   (((x) & 0x0000ff) >>  0)
#define CLR_16(x)  ((double)(x) / 0xff)
#define CLR_GDK(x) (const GdkRGBA)  .red = CLR_16(CLR_R(x)), \
                                    .green = CLR_16(CLR_G(x)), \
                                    .blue = CLR_16(CLR_B(x)), \
                                    .alpha = 0  
vte_terminal_set_colors(VTE_TERMINAL(terminal),
    &CLR_GDK(0xffffff),
    &(GdkRGBA)  .alpha = 0.85  ,
    (const GdkRGBA[]) 
        CLR_GDK(0x111111),
        CLR_GDK(0xd36265),
        CLR_GDK(0xaece91),
        CLR_GDK(0xe7e18c),
        CLR_GDK(0x5297cf),
        CLR_GDK(0x963c59),
        CLR_GDK(0x5E7175),
        CLR_GDK(0xbebebe),
        CLR_GDK(0x666666),
        CLR_GDK(0xef8171),
        CLR_GDK(0xcfefb3),
        CLR_GDK(0xfff796),
        CLR_GDK(0x74b8ef),
        CLR_GDK(0xb85e7b),
        CLR_GDK(0xA3BABF),
        CLR_GDK(0xffffff)
 , 16);

While you can t see it on the screenshot¹, this also enables background transparency.

Miscellaneous settings VTE comes with many settings to change the behavior of the terminal. Consider the following code:

vte_terminal_set_scrollback_lines(VTE_TERMINAL(terminal), 0);
vte_terminal_set_scroll_on_output(VTE_TERMINAL(terminal), FALSE);
vte_terminal_set_scroll_on_keystroke(VTE_TERMINAL(terminal), TRUE);
vte_terminal_set_rewrap_on_resize(VTE_TERMINAL(terminal), TRUE);
vte_terminal_set_mouse_autohide(VTE_TERMINAL(terminal), TRUE);

This will:

• disable the scrollback buffer,
• not scroll to the bottom on new output,
• scroll to the bottom on keystroke,
• rewrap content when terminal size change, and
• hide the mouse cursor when typing.

Update the window title An application can change the window title using XTerm control sequences (for example, with printf "\e]2;$ title \a"). If you want the actual window title to reflect this, you need to define this function:

static gboolean
on_title_changed(GtkWidget *terminal, gpointer user_data)
 
    GtkWindow *window = user_data;
    gtk_window_set_title(window,
        vte_terminal_get_window_title(VTE_TERMINAL(terminal))?:"Terminal");
    return TRUE;
 

Then, connect it to the appropriate signal, in main():

g_signal_connect(terminal, "window-title-changed", 
    G_CALLBACK(on_title_changed), GTK_WINDOW(window));

Final words I don t need much more as I am using tmux inside each terminal. In my own copy, I have also added the ability to complete a word using ones from the current window or other windows (also known as dynamic abbrev expansion). This requires to implement a terminal daemon to handle all terminal windows with one process, similar to urxvtcd. While writing a terminal from scratch ² suits my need, it may not be worth it. evilvte is quite customizable and can be lightweight. Consider it as a first alternative. Honestly, I don t remember why I didn t pick it. UPDATED: evilvte has not seen an update since 2014. Its GTK+3 support is buggy. It doesn t support the latest versions of the VTE library. Therefore, it s not a good idea to use it. You should also note that the primary goal of VTE is to be a library to support GNOME Terminal. Notably, if a feature is not needed for GNOME Terminal, it won t be added to VTE. If it already exists, it will likely to be deprecated and removed.

---

1. Transparency is handled by the composite manager (Compton, in my case).
2. For some definition of scratch since the hard work is handled by VTE.

Regular backups seem to also only be taken once per 24 hours, though team-member-1 has not yet been able to figure out where they are stored. According to team-member-2 these don t appear to be working, producing files only a few bytes in size.

$ backupchecker -G database-dump.tar.gz
$ cat database-dump.list
[archive]
mtime  1486480274.2923253
[files]
database.sql  =7854803 uid 1000 gid 1000 owner chaica group chaica mode 644 type f mtime 1486480253.0

[files]
database.sql  >6m uid 1000 gid 1000 mode 644 type f

$ touch /tmp/database.sql && \
tar zcvf /tmp/database-dump.tar.gz /tmp/database.sql && \
cp /tmp/database-dump.tar.gz .

$ backupchecker -C database-dump.conf
$ cat a.out 
WARNING:root:1 file smaller than expected while checking /tmp/article-backup-checker/database-dump.tar.gz: 
WARNING:root:database.sql size is 0. Should have been bigger than 6291456.

• The Backup Checker project on Github
• The official documentation of the Backup Checker project on Readthedocs.

Project structure For a standalone project, vendoring is a must-have¹ as you cannot rely on your dependencies to not introduce backward-incompatible changes. Some packages are using versioned URLs but most of them aren t. There is currently no standard tool to handle vendoring. My personal take is to vendor all dependencies with Glide. It is a good practice to split an application into different packages while the main one stay fairly small. In the hellogopher example, the CLI is handled in the cmd package while the application logic for printing greetings is in the hello package:

.
  cmd/
    hello.go
    root.go
    version.go
  glide.lock (generated)
  glide.yaml
  vendor/ (dependencies will go there)
  hello/
    root.go
    root_test.go
  main.go
  Makefile
  README.md

Down the rabbit hole Let s take a look at the various features of the Makefile.

GOPATH handling Since all dependencies are vendored, only our own project needs to be in the GOPATH:

PACKAGE  = hellogopher
GOPATH   = $(CURDIR)/.gopath
BASE     = $(GOPATH)/src/$(PACKAGE)
$(BASE):
    @mkdir -p $(dir $@)
    @ln -sf $(CURDIR) $@

The base import path is hellogopher, not github.com/vincentbernat/hellogopher: this shortens imports and makes them easily distinguishable from imports of dependency packages. However, your application won t be go get-able. This is a personal choice and can be adjusted with the $(PACKAGE) variable. We just create a symlink from .gopath/src/hellogopher to our root directory. The GOPATH environment variable is automatically exported to the shell commands of the recipes. Any tool should work fine after changing the current directory to $(BASE). For example, this snippet builds the executable:

.PHONY: all
all:   $(BASE)
    cd $(BASE) && $(GO) build -o bin/$(PACKAGE) main.go

Vendoring dependencies Glide is a bit like Ruby s Bundler. In glide.yaml, you specify what packages you need and the constraints you want on them. Glide computes a glide.lock file containing the exact versions for each dependencies (including recursive dependencies) and download them in the vendor/ folder. I choose to check into the VCS both glide.yaml and glide.lock files. It s also possible to only check in the first one or to also check in the vendor/ directory. A work-in-progress is currently ongoing to provide a standard dependency management tool with a similar workflow. We define two rules²:

GLIDE = glide
glide.lock: glide.yaml   $(BASE)
    cd $(BASE) && $(GLIDE) update
    @touch $@
vendor: glide.lock   $(BASE)
    cd $(BASE) && $(GLIDE) --quiet install
    @ln -sf . vendor/src
    @touch $@

We use a variable to invoke glide. This enables a user to easily override it (for example, with make GLIDE=$GOPATH/bin/glide).

Using third-party tools Most projects need some third-party tools. We can either expect them to be already installed or compile them in our private GOPATH. For example, here is the lint rule:

BIN    = $(GOPATH)/bin
GOLINT = $(BIN)/golint
$(BIN)/golint:   $(BASE) #  
    go get github.com/golang/lint/golint
.PHONY: lint
lint: vendor   $(BASE) $(GOLINT) #  
    @cd $(BASE) && ret=0 && for pkg in $(PKGS); do \
        test -z "$$($(GOLINT) $$pkg   tee /dev/stderr)"   ret=1 ; \
     done ; exit $$ret

As for glide, we let the user a chance to override which golint executable to use. By default, it uses a private copy. But a user can use its own copy with make GOLINT=/usr/bin/golint. In , we have the recipe to build the private copy. We simply issue go get³ to download and build golint. In , the lint rule executes golint on each package contained in the $(PKGS) variable. We ll explain this variable in the next section.

Working with non-vendored packages only Some commands need to be provided with a list of packages. Because we use a vendor/ directory, the shortcut ./... is not what we expect as we don t want to run tests on our dependencies⁴. Therefore, we compose a list of packages we care about:

PKGS = $(or $(PKG), $(shell cd $(BASE) && \
    env GOPATH=$(GOPATH) $(GO) list ./...   grep -v "^$(PACKAGE)/vendor/"))

If the user has provided the $(PKG) variable, we use it. For example, if they want to lint only the cmd package, they can invoke make lint PKG=hellogopher/cmd which is more intuitive than specifying PKGS. Otherwise, we just execute go list ./... but we remove anything from the vendor directory.

Tests Here are some rules to run tests:

TIMEOUT = 20
TEST_TARGETS := test-default test-bench test-short test-verbose test-race
.PHONY: $(TEST_TARGETS) check test tests
test-bench:   ARGS=-run=__absolutelynothing__ -bench=.
test-short:   ARGS=-short
test-verbose: ARGS=-v
test-race:    ARGS=-race
$(TEST_TARGETS): test
check test tests: fmt lint vendor   $(BASE)
    @cd $(BASE) && $(GO) test -timeout $(TIMEOUT)s $(ARGS) $(PKGS)

A user can invoke tests in different ways:

• make test runs all tests;
• make test TIMEOUT=10 runs all tests with a timeout of 10 seconds;
• make test PKG=hellogopher/cmd only runs tests for the cmd package;
• make test ARGS="-v -short" runs tests with the specified arguments;
• make test-race runs tests with race detector enabled.

Tests coverage go test includes a test coverage tool. Unfortunately, it only handles one package at a time and you have to explicitely list the packages to be instrumented, otherwise the instrumentation is limited to the currently tested package. If you provide too many packages, the compilation time will skyrocket. Moreover, if you want an output compatible with Jenkins, you ll need some additional tools.

COVERAGE_MODE    = atomic
COVERAGE_PROFILE = $(COVERAGE_DIR)/profile.out
COVERAGE_XML     = $(COVERAGE_DIR)/coverage.xml
COVERAGE_HTML    = $(COVERAGE_DIR)/index.html
.PHONY: test-coverage test-coverage-tools
test-coverage-tools:   $(GOCOVMERGE) $(GOCOV) $(GOCOVXML) #  
test-coverage: COVERAGE_DIR := $(CURDIR)/test/coverage.$(shell date -Iseconds)
test-coverage: fmt lint vendor test-coverage-tools   $(BASE)
    @mkdir -p $(COVERAGE_DIR)/coverage
    @cd $(BASE) && for pkg in $(PKGS); do \ #  
        $(GO) test \
            -coverpkg=$$($(GO) list -f '  join .Deps "\n"  ' $$pkg   \
                    grep '^$(PACKAGE)/'   grep -v '^$(PACKAGE)/vendor/'   \
                    tr '\n' ',')$$pkg \
            -covermode=$(COVERAGE_MODE) \
            -coverprofile="$(COVERAGE_DIR)/coverage/ echo $$pkg   tr "/" "-" .cover" $$pkg ;\
     done
    @$(GOCOVMERGE) $(COVERAGE_DIR)/coverage/*.cover > $(COVERAGE_PROFILE)
    @$(GO) tool cover -html=$(COVERAGE_PROFILE) -o $(COVERAGE_HTML)
    @$(GOCOV) convert $(COVERAGE_PROFILE)   $(GOCOVXML) > $(COVERAGE_XML)

First, we define some variables to let the user override them. We also require the following tools (in ):

• gocovmerge merges profiles from different runs into a single one;
• gocov-xml converts a coverage profile to the Cobertura format;
• gocov is needed to convert a coverage profile to a format handled by gocov-xml.

The rules to build those tools are similar to the rule for golint described a few sections ago. In , for each package to test, we run go test with the -coverprofile argument. We also explicitely provide the list of packages to instrument to -coverpkg by using go list to get a list of dependencies for the tested package and keeping only our owns.

Final result While the main goal of using a Makefile was to work around GOPATH, it s also a good place to hide the complexity of some operations, notably around test coverage. The excerpts provided in this post are a bit simplified. Have a look at the final result for more perks!

---

1. In Go, vendoring is about both bundling and dependency management. As the Go ecosystem matures, the bundling part (fixed snapshots of dependencies) may become optional but the vendor/ directory may stay for dependency management (retrieval of the latest versions of dependencies matching a set of constraints).
2. If you don t want to automatically update glide.lock when a change is detected in glide.yaml, rename the target to deps-update and make it a phony target.
3. There is some irony for bad mouthing go get and then immediately use it because it is convenient.
4. I think ./... should not include the vendor/ directory by default. Dependencies should be trusted to have run their own tests in the environment they expect them to succeed. Unfortunately, this is unlikely to change.

Request an additional IPv6 block The first thing you need to do is get a new IPv6 address block (or "pool" as Linode calls it) from which you can allocate a single address to each VPN client that connects to the server. If you are using a Linode VPS, there are instructions on how to request a new IPv6 pool. Note that you need to get an address block between /64 and /112. A /116 like Linode offers won't work in OpenVPN. Thankfully, Linode is happy to allocate you an extra /64 for free.

Setup the new IPv6 address If your server only has an single IPv4 address and a single IPv6 address, then a simple DHCP-backed network configuration will work fine. To add the second IPv6 block on the other hand, I had to change my network configuration (/etc/network/interfaces) to this:

auto lo
iface lo inet loopback
allow-hotplug eth0
iface eth0 inet dhcp
    pre-up iptables-restore /etc/network/iptables.up.rules
iface eth0 inet6 static
    address 2600:3c01::xxxx:xxxx:xxxx:939f/64
    gateway fe80::1
    pre-up ip6tables-restore /etc/network/ip6tables.up.rules
iface tun0 inet6 static
    address 2600:3c01:xxxx:xxxx::/64
    pre-up ip6tables-restore /etc/network/ip6tables.up.rules

where 2600:3c01::xxxx:xxxx:xxxx:939f/64 (bound to eth0) is your main IPv6 address and 2600:3c01:xxxx:xxxx::/64 (bound to tun0) is the new block you requested. Once you've setup the new IPv6 block, test it from another IPv6-enabled host using:

ping6 2600:3c01:xxxx:xxxx::1

OpenVPN configuration The only thing I had to change in my OpenVPN configuration (/etc/openvpn/server.conf) was to change:

proto udp

to:

proto udp6

in order to make the VPN server available over both IPv4 and IPv6, and to add the following lines:

server-ipv6 2600:3c01:xxxx:xxxx::/64
push "route-ipv6 2000::/3"

to bind to the right V6 address and to tell clients to tunnel all V6 Internet traffic through the VPN. In addition to updating the OpenVPN config, you will need to add the following line to /etc/sysctl.d/openvpn.conf:

net.ipv6.conf.all.forwarding=1

and the following to your firewall (e.g. /etc/network/ip6tables.up.rules):

# openvpn
-A INPUT -p udp --dport 1194 -j ACCEPT
-A FORWARD -m state --state NEW -i tun0 -o eth0 -s 2600:3c01:xxxx:xxxx::/64 -j ACCEPT
-A FORWARD -m state --state NEW -i eth0 -o tun0 -d 2600:3c01:xxxx:xxxx::/64 -j ACCEPT
-A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

in order to ensure that IPv6 packets are forwarded from the eth0 network interface to tun0 on the VPN server. With all of this done, apply the settings by running:

sysctl -p /etc/sysctl.d/openvpn.conf
ip6tables-apply
systemctl restart openvpn.service

Testing the connection Now connect to the VPN using your desktop client and check that the default IPv6 route is set correctly using ip -6 route. Then you can ping the server's new IP address:

ping6 2600:3c01:xxxx:xxxx::1

and from the server, you can ping the client's IP (which you can see in the network settings):

ping6 2600:3c01:xxxx:xxxx::1002

Once both ends of the tunnel can talk to each other, you can try pinging an IPv6-only server from your client:

ping6 ipv6.google.com

and then pinging your client from an IPv6-enabled host somewhere:

ping6 2600:3c01:xxxx:xxxx::1002

If that works, other online tests should also work.