2022-08-20  coffee
    family:liabilities:creditcard     -3
    jon:expenses:coffee                3

2022-08-20  coffee
    family:liabilities:creditcard     -3
    family:liabilities:jon             3 ; jon owes family

When you accidentally use the family CV for personal expenses, credit the account "family:liabilities:creditcard:jon" instead of "family:liabilities:creditcard". That'll allow you to track w/ 2 postings.

$ hledger bal -t
              -3  family:liabilities:creditcard
               3  jon:expenses:coffee

2022-08-20  coffee
    family:liabilities:creditcard:jon     -3
    jon:expenses:coffee                    3

$ hledger bal -t
              -3  family:liabilities:creditcard
              -3    jon
               3  jon:expenses:coffee

Else, add: family:assets:receivable:jon $3
jon:liabilities:family:cc $-3

2022-08-20  coffee
    family:liabilities:creditcard     -3
    jon:expenses:coffee                3
    family:assets:receivable:jon       3
    jon:liabilities:family            -3

jon:liabilities:family    -3

• [ELA-643-1] for ncurses (5.9+20140913-1+deb8u4, 6.0+20161126-1+deb9u3)
• [ELA-655-1] for libhttp-daemon-perl (6.01-1+deb8u1, 6.01-1+deb9u1)
• [6.14-1.1] upload to unstable
• [#1016391] bullseye-pu: libhttp-daemon-perl/6.12-1+deb11u1

• meep
• meep-openmpi
• meep-mpi-default
• glewlwyd
• entropybroker

Little background I never liked tea much. I am also not a coffee person either. But if I have to choose over two that will be coffee because of the strong aroma. Going to relatives house, they always offered hot tea defacto. I always find difficult say no to their friendly gesture. But I hate tea. A generation before me drinks lot of tea here at my place. You can see tea stalls in every corner and people sipping tea. I always wondered why people drink lot of tea on a hot country like India. The book I am currently trying to read has a chapter about Munnar and how it became a Tea plantation under the British rule. Well, around the same time. I watched a documentary program about the tea and Munnar.

Munnar Too much word here and there I decided to do a visit. I took a motorbike and started a journey to Munnar. Due to covid restrictions there weren t much tourists, so this was to my advantage. There are many water falls on the way to Munnar. Some are very close to road and some are far away but can be spotted. Munnar travel is just not about the destination because its never been a single spot. Enjoying the journey that the ride has to offer. I stayed at a hotel, little far away from town, though I never recommend hotels in Munnar. Try to find home stays and small establishments away from the town. There are British Era bungalows inside the plantations still maintained in good condition which can be booked per room or entire property. The lush greenery on the Mountains of tea plantation is very refreshing and feast to our eyes. The mornings and evenings of Munnar is something to watch, mountains wrapped in mist slowly uncovering with sunlight and again slipping to mist by dark evening. I planned only to visit places which are less explored by tourists. People here live a simple life. Most of them are plantation workers. The native people of Munnar are actually tribal folks but since the plantation boom many people from Tamil Nadu(neighboring state) and other parts of Kerala settled here. The houses of this plantation workers resembled Hobbit homes in Shire from Lord of the Rings as they are in the hill slides. The Kannan Devan hills, the biggest hill in area covers more than half of Munnar. Two famous Tea companies from Munnar are Tata Tea and KDHP(Kanan Devan Hills Plantations Company (P) Limited) tea. KDHP is actually an employee owned Tea company ie a good share of this company is owned by the employees working there. This was interesting to me, so I bought a bag of speciality tea from KDHP store on my return. I don t drink tea on a daily basis but I will try it on special occasions.

• [1] http://tinyurl.com/244zutnz
• [2] https://rorodi.substack.com/p/the-biggest-crypto-lending-company
• [3] https://tinyurl.com/2c4m3z5u
• [4] https://tinyurl.com/25mtjxf4
• [5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2980962/
• [6] https://tinyurl.com/yavs2wow

• it increases the chances of breaking the OS, and
• any changes will disappear with the next OS update.

$ qemu-system-x86_64 -enable-kvm -smp cores=4 -m 8G \
    -device usb-ehci -device usb-tablet \
    -device intel-hda -device hda-duplex \
    -device VGA,xres=1280,yres=800 \
    -drive if=pflash,format=raw,readonly=on,file=/usr/share/ovmf/OVMF.fd \
    -drive if=virtio,file=steamdeck-recovery-4.img,driver=raw \
    -device nvme,drive=drive0,serial=badbeef \
    -drive if=none,id=drive0,file=steamos.qcow2

$ sudo steamos-chroot --disk /dev/nvme0n1 --partset A
# steamos-readonly disable
# echo '[Autologin]' > /etc/sddm.conf.d/zz-steamos-autologin.conf
# echo 'Session=plasma.desktop' >> /etc/sddm.conf.d/zz-steamos-autologin.conf
# steamos-readonly enable
# exit
$ sudo steamos-chroot --disk /dev/nvme0n1 --partset B
# steamos-readonly disable
# echo '[Autologin]' > /etc/sddm.conf.d/zz-steamos-autologin.conf
# echo 'Session=plasma.desktop' >> /etc/sddm.conf.d/zz-steamos-autologin.conf
# steamos-readonly enable
# exit

$ cp /usr/share/OVMF/OVMF_VARS.fd .
$ qemu-system-x86_64 -enable-kvm -smp cores=4 -m 8G \
   -device usb-ehci -device usb-tablet \
   -device intel-hda -device hda-duplex \
   -device VGA,xres=1280,yres=800 \
   -drive if=pflash,format=raw,readonly=on,file=/usr/share/ovmf/OVMF.fd \
   -drive if=pflash,format=raw,file=OVMF_VARS.fd \
   -drive if=virtio,file=steamos.qcow2 \
   -device virtio-net-pci,netdev=net0 \
   -netdev user,id=net0,hostfwd=tcp::2222-:22

• (optional) Change the keyboard layout in the system settings (the default one is US English)
• Set the password for the deck user: run passwd on a terminal
• Enable / start the SSH server: sudo systemctl enable sshd and/or sudo systemctl start sshd .
• SSH into the machine: ssh -p 2222 deck@localhost

• First of all ensure that you re giving enought RAM to the VM (in my examples I run QEMU with -m 8G). The OS update might fail if you use less.
• (optional) Change the OS branch if you want to try the beta release: sudo steamos-select-branch beta (or main, if you want the bleeding edge)
• Check the currently installed version in /etc/os-release (see the BUILD_ID variable)
• Check the available version: steamos-update check
• Download and install the software update: steamos-update

$ sudo steamos-chroot --partset other
# steamos-readonly disable
# echo '[Autologin]' > /etc/sddm.conf.d/zz-steamos-autologin.conf
# echo 'Session=plasma.desktop' >> /etc/sddm.conf.d/zz-steamos-autologin.conf
# steamos-readonly enable
# exit

Server setup The first thing I did was to open up my server's rsyslog (Debian's default syslog server) to remote connections since it's going to be the destination host for the router's log messages. I added the following to /etc/rsyslog.d/router.conf:

module(load="imtcp")
input(type="imtcp" port="514")
if $fromhost-ip == '192.168.1.1' then  
    if $syslogseverity <= 5 then  
        action(type="omfile" file="/var/log/router.log")
     
    stop
 

This is using the latest rsyslog configuration method: a handy scripting language called RainerScript. Severity level 5 maps to "notice" which consists of unusual non-error conditions, and 192.168.1.1 is of course the IP address of the router on the LAN side. With this, I'm directing all router log messages to a separate file, filtering out anything less important than severity 5. In order for rsyslog to pick up this new configuration file, I restarted it:

systemctl restart rsyslog.service

and checked that it was running correctly (e.g. no syntax errors in the new config file) using:

systemctl status rsyslog.service

Since I added a new log file, I also setup log rotation for it by putting the following in /etc/logrotate.d/router:

/var/log/router.log
 
    rotate 4
    weekly
    missingok
    notifempty
    compress
    delaycompress
    sharedscripts
    postrotate
        /usr/lib/rsyslog/rsyslog-rotate
    endscript
 

In addition, since I use logcheck to monitor my server logs and email me errors, I had to add /var/log/router.log to /etc/logcheck/logcheck.logfiles. Finally I opened the rsyslog port to the router in my server's firewall by adding the following to /etc/network/iptables.up.rules:

# Allow logs from the router
-A INPUT -s 192.168.1.1 -p tcp --dport 514 -j ACCEPT

and ran iptables-apply. With all of this in place, it was time to get the router to send messages.

Router setup As suggested on the Turris forum, I ssh'ed into my router and added this in /etc/syslog-ng.d/remote.conf:

destination d_loghost  
        network("192.168.1.200" time-zone("America/Vancouver"));
 ;
source dns  
        file("/var/log/resolver");
 ;
log  
        source(src);
        source(net);
        source(kernel);
        source(dns);
        destination(d_loghost);
 ;

Setting the timezone to the same as my server was needed because the router messages were otherwise sent with UTC timestamps. To ensure that the destination host always gets the same IP address (192.168.1.200), I went to the advanced DHCP configuration page and added a static lease for the server's MAC address so that it always gets assigned 192.168.1.200. If that wasn't already the server's IP address, you'll have to restart it for this to take effect. Finally, I restarted the syslog-ng daemon on the router to pick up the new config file:

/etc/init.d/syslog-ng restart

Testing In order to test this configuration, I opened three terminal windows:

1. tail -f /var/log/syslog on the server
2. tail -f /var/log/router.log on the server
3. tail -f /var/log/messages on the router

I immediately started to see messages from the router in the third window and some of these, not all because of my severity-5 filter, were flowing to the second window as well. Also important is that none of the messages make it to the first window, otherwise log messages from the router would be mixed in with the server's own logs. That's the purpose of the stop command in /etc/rsyslog.d/router.conf. To force a log messages to be emitted by the router, simply ssh into it and issue the following command:

logger Test

It should show up in the second and third windows immediately if you've got everything setup correctly

It seems that in every attack Dickens makes upon society he is always pointing to a change of spirit rather than a change of structure. It is hopeless to try and pin him down to any definite remedy, still more to any political doctrine. His approach is always along the moral plane, and his attitude is sufficiently summed up in that remark about Strong's school being as different from Creakle's "as good is from evil." Two things can be very much alike and yet abysmally different. Heaven and Hell are in the same place. Useless to change institutions without a "change of heart" that, essentially, is what he is always saying. If that were all, he might be no more than a cheer-up writer, a reactionary humbug. A "change of heart" is in fact the alibi of people who do not wish to endanger the status quo. But Dickens is not a humbug, except in minor matters, and the strongest single impression one carries away from his books is that of a hatred of tyranny.

His radicalism is of the vaguest kind, and yet one always knows that it is there. That is the difference between being a moralist and a politician. He has no constructive suggestions, not even a clear grasp of the nature of the society he is attacking, only an emotional perception that something is wrong, all he can finally say is, "Behave decently," which, as I suggested earlier, is not necessarily so shallow as it sounds. Most revolutionaries are potential Tories, because they imagine that everything can be put right by altering the shape of society; once that change is effected, as it sometimes is, they see no need for any other. Dickens has not this kind of mental coarseness. The vagueness of his discontent is the mark of its permanence. What he is out against is not this or that institution, but, as Chesterton put it, "an expression on the human face."

Why did I bother? My needs arose primarily from handling Backups over Asynchronous Communication methods in this case, NNCP. When backups contain incrementals that are unpacked on the destination, they must be applied in the correct order. In some cases, like ZFS, the receiving side will detect an out-of-order backup file and exit with an error. In those cases, processing in random order is acceptable but can be slow if, say, hundreds or thousands of hourly backups have stacked up over a period of time. The same goes for using gitsync-nncp to synchronize git repositories. In both cases, a best effort based on creation date is sufficient to produce a significant performance improvement. With other cases, such as tar or dar backups, the receiving cannot detect out of order incrementals. In those situations, the incrementals absolutely must be applied with strict ordering. There are many other situations that arise with these needs also. Filespooler is the answer to these.

Existing Work Before writing my own program, I of course looked at what was out there already. I looked at celeary, gearman, nq, rq, cctools work queue, ts/tsp (task spooler), filequeue, dramatiq, GNU parallel, and so forth. Unfortunately, none of these met my needs at all. They all tended to have properties like:

• An extremely complicated client/server system that was incompatible with piping data over existing asynchronous tools
• A large bias to processing of small web requests, resulting in terrible inefficiency or outright incompatibility with jobs in the TB range
• An inability to enforce strict ordering of jobs, especially if they arrive in a different order from how they were queued

Many also lacked some nice-to-haves that I implemented for Filespooler:

• Support for the encryption and cryptographic authentication of jobs, including metadata
• First-class support for arbitrary compressors
• Ability to use both stream transports (pipes) and filesystem-like transports (eg, rclone mount, S3, Syncthing, or Dropbox)

Introducing Filespooler Filespooler is a tool in the Unix tradition: that is, do one thing well, and integrate nicely with other tools using the fundamental Unix building blocks of files and pipes. Filespooler itself doesn t provide transport for jobs, but instead is designed to cooperate extremely easily with transports that can be written to as a filesystem or piped to which is to say, almost anything of interest. Filespooler is written in Rust and has an extensive Filespooler Reference as well as many tutorials on its homepage. To give you a few examples, here are some links:

• Using Filespooler over Syncthing (and the most comprehensive tutorial)
• Using Filespooler over NNCP
• Compressing Filespooler Jobs
• Encrypting Filespooler Jobs with GPG or Age
• Guidelines for Writing To Filespooler Queues Without Using Filespooler

Basics of How it Works Filespooler is intentionally simple:

• The sender maintains a sequence file that includes a number for the next job packet to be created.
• The receiver also maintains a sequence file that includes a number for the next job to be processed.
• fspl prepare creates a Filespooler job packet and emits it to stdout. It includes a small header (<100 bytes in most cases) that includes the sequence number, creation timestamp, and some other useful metadata.
• You get to transport this job packet to the receiver in any of many simple ways, which may or may not involve Filespooler s assistance.
• On the receiver, Filespooler (when running in the default strict ordering mode) will simply look at the sequence file and process jobs in incremental order until it runs out of jobs to process.

The name of job files on-disk matches a pattern for identification, but the content of them is not significant; only the header matters. You can send job data in three ways:

1. By piping it to fspl prepare
2. By setting certain environment variables when calling fspl prepare
3. By passing additional command-line arguments to fspl prepare, which can optionally be passed to the processing command at the receiver.

Data piped in is added to the job payload , while environment variables and command-line parameters are encoded in the header.

Basic usage Here I will excerpt part of the Using Filespooler over Syncthing tutorial; consult it for further detail. As a bit of background, Syncthing is a FLOSS decentralized directory synchronization tool akin to Dropbox (but with a much richer feature set in many ways).

Preparation First, on the receiver, you create the queue (passing the directory name to -q):

sender$ fspl queue-init -q ~/sync/b64queue

Now, we can send a job like this:

sender$ echo Hi   fspl prepare -s ~/b64seq -i -   fspl queue-write -q ~/sync/b64queue

Let s break that down:

• First, we pipe Hi to fspl prepare.
• fspl prepare takes two parameters:
  • -s seqfile gives the path to a sequence file used on the sender side. This file has a simple number in it that increments a unique counter for every generated job file. It is matched with the nextseq file within the queue to make sure that the receiver processes jobs in the correct order. It MUST be separate from the file that is in the queue and should NOT be placed within the queue. There is no need to sync this file, and it would be ideal to not sync it.
  • The -i option tells fspl prepare to read a file for the packet payload. -i - tells it to read stdin for this purpose. So, the payload will consist of three bytes: Hi\n (that is, including the terminating newline that echo wrote)
• Now, fspl prepare writes the packet to its stdout. We pipe that into fspl queue-write:
  • fspl queue-write reads stdin and writes it to a file in the queue directory in a safe manner. The file will ultimately match the fspl-*.fspl pattern and have a random string in the middle.

At this point, wait a few seconds (or however long it takes) for the queue files to be synced over to the recipient. On the receiver, we can see if any jobs have arrived yet:

receiver$ fspl queue-ls -q ~/sync/b64queue
ID                   creation timestamp          filename
1                    2022-05-16T20:29:32-05:00   fspl-7b85df4e-4df9-448d-9437-5a24b92904a4.fspl

Let s say we d like some information about the job. Try this:

receiver$ $ fspl queue-info -q ~/sync/b64queue -j 1
FSPL_SEQ=1
FSPL_CTIME_SECS=1652940172
FSPL_CTIME_NANOS=94106744
FSPL_CTIME_RFC3339_UTC=2022-05-17T01:29:32Z
FSPL_CTIME_RFC3339_LOCAL=2022-05-16T20:29:32-05:00
FSPL_JOB_FILENAME=fspl-7b85df4e-4df9-448d-9437-5a24b92904a4.fspl
FSPL_JOB_QUEUEDIR=/home/jgoerzen/sync/b64queue
FSPL_JOB_FULLPATH=/home/jgoerzen/sync/b64queue/jobs/fspl-7b85df4e-4df9-448d-9437-5a24b92904a4.fspl

This information is intentionally emitted in a format convenient for parsing. Now let s run the job!

receiver$ fspl queue-process -q ~/sync/b64queue --allow-job-params base64
SGkK

There are two new parameters here:

• --allow-job-params says that the sender is trusted to supply additional parameters for the command we will be running.
• base64 is the name of the command that we will run for every job. It will:
  • Have environment variables set as we just saw in queue-info
  • Have the text we previously prepared Hi\n piped to it

By default, fspl queue-process doesn t do anything special with the output; see Handling Filespooler Command Output for details on other options. So, the base64-encoded version of our string is SGkK . We successfully sent a packet using Syncthing as a transport mechanism! At this point, if you do a fspl queue-ls again, you ll see the queue is empty. By default, fspl queue-process deletes jobs that have been successfully processed.

For more See the Filespooler homepage.

---

This blog post is also available as a permanent, periodically-updated page.

The internet, it s that thing that acts up all the time, right? As said in my first post, I abandoned the idea to interview children younger than 9 years because it seems they are not necessarily aware that they are using the internet. But it turns out that some do have heard about the internet. My friend Anna, who has 9 younger siblings, tried to win some of her brothers and sisters for an interview with me. At the dinner table, this turned into a discussion and she sent me an incredibly funny video where two of her brothers and sisters, aged 5 and 6, discuss with her about the internet. I won t share the video for privacy reasons besides, the kids speak in the wondrous dialect of Vorarlberg, a region in western Austria, close to the border with Liechtenstein. Here s a transcription of the dinner table discussion:

• Anna: what is the internet?
• both children: (shouting as if it was a game of who gets it first) photo! mobile! device! camera!
• Anna: But one can have a camera without the internet
• M.: Internet is the mobile phone charger! Mobile phone full!
• J.: Internet is internet is
• M.: I know! Internet is where you can charge something, the mobile phone and
• Anna: You mean electricity?
• M.: Yeah, that is the internet, electricity!
• Anna: (laughs), Yes, the internet works a bit similarly, true.
• J.: It s the electricity of the house!
• Anna: The electricity of the house

(everyone is talking at the same time now.)

• Anna: And what s WiFi?
• M.: WiFi it s the TV!
• Anna (laughs)
• M.: WiFi is there so it doesn t act up!
• Anna (laughs harder)
• J. (repeats what M. just said): WiFi is there so it doesn t act up!
• Anna: So that what doesn t act up?
• M.: (moves her finger wildly drawing a small circle in the air) So that it doesn t spin!
• Anna: Ah?
• M.: When one wants to watch something on Youtube, well then that the thing doesn t spin like that!
• Anna: Ahhh! so when you use Youtube, you need the internet, right?
• J.: Yes, so that one can watch things.

I really like how the kids associate the internet with a thing that works all the time, except for when it doesn t work. Then they notice: The internet is acting up! Probably, when that happens, parents or older siblings say: the internet is acting up or let me check why the internet acts up again and maybe they get up from the sofa, switch a home router on and off again, which creates this association with electricity. (Just for the sake of clarity for fellow multilingualist readers, the kids used the German word spinnen , which I translated to acting up . In French that would be d conner .)

WiFi for everyone! I interviewed another of Anna s siblings, a 10 year old boy. He told me that he does not really use the internet by himself yet, and does not own any internet capable device. He watches when older family members look up stuff on Google, or put on a video on Youtube, Netflix, or Amazon he knew all these brand names though. In the living room, there s Alexa, he told me, and he uses the internet by asking Alexa to play music.

Then I say: Alexa, play this song!

Interestingly, he knew that, in order to listen to a CD, the internet was not needed. When asked how a drawing would look like that explains the internet, he drew a scheme of the living room at home, with the TV, Alexa, and some kind of WiFi dongle, maybe a repeater. (Unfortunately I did not manage to get his drawing.) If he could ask a wise and friendly dragon one thing about the internet that he always wanted to know, he would ask How much internet can one have and what are all the things one can do with the internet? If he could change the internet for the better for everyone, he would build a gigantic building which would provide the entire world with WiFi.

Cut out the stupid stuff from the internet His slightly older sister does own a laptop and a smartphone. She uses the internet to watch movies, or series, to talk with her friends, or to listen to music. When asked how she would explain the internet to an alien, she said that

one can do a lot of things on the internet, but on the internet there can be stupid things, but also good things, one can learn stuff on the internet, for example how to do crochet.

Most importantly, she noticed that

one needs the internet nowadays.

Her drawing shows how she uses the internet: calls using WhatsApp, watching movies online, and a laptop with open windows on the screen. She would ask the dragon that can explain one thing she always wanted to know about the internet:

What is the internet? How does it work at all? How does it function?

What she would change has to do with her earlier remark about stupid things:

I would make it so that there are less stupid things. It would be good to use the internet for better things, but not for useless things, that one doesn t actually need.

When I asked her what she meant by stupid things , she replied:

Useless videos where one talks about nonsense. And one can also google stupid things, for example how long will i be alive? and stuff like that.

Patterns From the interviews I made until now, there seems to be a cut between then age where kids don t own a device and use the internet to watch movies, series or listen to music and the age where they start owning a device and then they start talking to their friends, and create accounts on social media. This seems to happen roughly at ages 9-10. I m still surprised at the amount of ideas that kids have, when asked what they would change on the internet if they could. I m sure there s more if one goes looking for it.

Thanks Thanks to my friends who made all these interviews possible either by allowing me to meet their children, or their younger siblings: Anna, Christa, Aline, Cindy, and Martina.

1. When you are trying to understand another religion, you should ask the adherents of that religion and not its enemies.
2. Don't compare your best to their worst.
3. Leave room for "holy envy."

POSIX and Coreutils Perhaps the trickiest use of the trailing slash in a distinguishing way is in POSIX² which states:

When the final component of a pathname is a symbolic link, the standard requires that a trailing <slash> causes the link to be followed. This is the behavior of historical implementations³. For example, for /a/b and /a/b/, if /a/b is a symbolic link to a directory, then /a/b refers to the symbolic link, and /a/b/ refers to the directory to which the symbolic link points.

This leads to some unexpected behavior. For example, if you have the following structure of a directory dir containing a file dirfile with a symbolic link link pointing to dir. (which will be used in all shell examples throughout this article):

$ ls -lR
.:
total 4
drwxr-xr-x 2 jacob jacob 4096 Apr  3 00:00 dir
lrwxrwxrwx 1 jacob jacob    3 Apr  3 00:00 link -> dir
./dir:
total 0
-rw-r--r-- 1 jacob jacob 0 Apr  3 00:12 dirfile

On Unixes such as MacOS, FreeBSD or Illumos⁴, you can move a directory through a symbolic link by using a trailing slash:

$ mv link/ otherdir
$ ls
link	otherdir

On Linux⁵, mv will not rename the indirectly referenced directory and not the symbolic link, when given a symbolic link with a trailing slash as the source to be renamed. despite the coreutils documentation s claims to the contrary⁶, instead failing with Not a directory:

$ mv link/ other
mv: cannot move 'link/' to 'other': Not a directory
$ mkdir otherdir
$ mv link/ otherdir
mv: cannot move 'link/' to 'otherdir/link': Not a directory
$ mv link/ otherdir/
mv: cannot move 'link/' to 'otherdir/link': Not a directory
$ mv link otherdirlink
$ ls -l otherdirlink
lrwxrwxrwx 1 jacob jacob 3 Apr  3 00:13 otherdirlink -> dir

This is probably for the best, as it is very confusing behavior. There is still one advantage the trailing slash has when using mv, even on Linux, in that is it does not allow you to move a file to a non-existent directory, or move a file that you expect to be a directory that isn t.

$ mv dir/dirfile nonedir/
mv: cannot move 'dir/dirfile' to 'nonedir/': Not a directory
$ touch otherfile
$ mv otherfile/ dir
mv: cannot stat 'otherfile/': Not a directory
$ mv otherfile dir
$ ls dir
dirfile  otherfile

However, Linux still exhibits some confusing behavior of its own, like when you attempt to remove link recursively with a trailing slash:

rm -rvf link/

Neither link nor dir are removed, but the contents of dir are removed:

removed 'link/dirfile'

Whereas if you remove the trailing slash, you just remove the symbolic link:

$ rm -rvf link
removed 'link'

While on MacOS, FreeBSD or Illumos⁴, rm will also remove the source directory:

$ rm -rvf link
link/dirfile
link/
$ ls
link

The find and ls commands, in contrast, behave the same on all three operating systems. The find command only searches the contents of the directory a symbolic link points to if the trailing slash is added:

$ find link -name dirfile
$ find link/ -name dirfile
link/dirfile

The ls command acts similarly, showing information on just a symbolic link by itself unless a trailing slash is added, at which point it shows the contents of the directory that it links to:

$ ls -l link
lrwxrwxrwx 1 jacob jacob 3 Apr  3 00:13 link -> dir
$ ls -l link/
total 0
-rw-r--r-- 1 jacob jacob 0 Apr  3 00:13 dirfile

rsync The command rsync handles a trailing slash in an unusual way that trips up many new users. The rsync man page notes:

You can think of a trailing / on a source as meaning copy the contents of this directory as opposed to copy the directory by name , but in both cases the attributes of the containing directory are transferred to the containing directory on the destination.

That is to say, if we had two folders a and b each of which contained some files:

$ ls -R .
.:
a  b
./a:
a1  a2
./b:
b1  b2

Running rsync -av a b moves the entire directory a to directory b:

$ rsync -av a b
sending incremental file list
a/
a/a1
a/a2
sent 181 bytes  received 58 bytes  478.00 bytes/sec
total size is 0  speedup is 0.00
$ ls -R b
b:
a  b1  b2
b/a:
a1  a2

While running rsync -av a/ b moves the contents of directory a to b:

$ rsync -av a/ b
sending incremental file list
./
a1
a2
sent 170 bytes  received 57 bytes  454.00 bytes/sec
total size is 0  speedup is 0.00
$ ls b
a1  a2	b1  b2

Dockerfile COPY The Dockerfile COPY command also cares about the presence of the trailing slash, using it to determine whether the destination should be considered a file or directory. The Docker documentation explains the rules of the command thusly:

COPY [--chown=<user>:<group>] <src>... <dest>

If <src> is a directory, the entire contents of the directory are copied, including filesystem metadata. Note: The directory itself is not copied, just its contents. If <src> is any other kind of file, it is copied individually along with its metadata. In this case, if <dest> ends with a trailing slash /, it will be considered a directory and the contents of <src> will be written at <dest>/base(<src>). If multiple <src> resources are specified, either directly or due to the use of a wildcard, then <dest> must be a directory, and it must end with a slash /. If <dest> does not end with a trailing slash, it will be considered a regular file and the contents of <src> will be written at <dest>. If <dest> doesn t exist, it is created along with all missing directories in its path.

This means if you had a COPY command that moved file to a nonexistent containerfile without the slash, it would create containerfile as a file with the contents of file.

COPY file /containerfile
container$ stat -c %F containerfile
regular empty file

Whereas if you add a trailing slash, then file will be added as a file under the new directory containerdir:

COPY file /containerdir/
container$ stat -c %F containerdir
directory

Interestingly, at no point can you copy a directory completely, only its contents. Thus if you wanted to make a directory in the new container, you need to specify its name in both the source and the destination:

COPY dir /dirincontainer
container$ stat -c %F /dirincontainer
directory

Dockerfiles do also make good use of the trailing slash to ensure they re doing what you mean by requiring a trailing slash on the destination of multiple files:

COPY file otherfile /othercontainerdir

results in the following error:

When using COPY with more than one source file, the destination must be a directory and end with a /

1. I m sure there are probably more than just these three cases, but these are the three I m familiar with. If you know of more, please tell me about them!.
2. Some additional relevant sections are the Path Resolution Appendix and the section on Symbolic Links.
3. The sentence This is the behavior of historical implementations implies that this probably originated in some ancient Unix derivative, possibly BSD or even the original Unix. I don t really have a source on that though, so please reach out if you happen to have any more knowledge on what this refers to.
4. I tested on MacOS 11.6.5, FreeBSD 12.0 and OmniOS 5.11 ²
5. unless the source is a directory trailing slashes give -ENOTDIR
6. In fairness to the coreutils maintainers, it seems to be true on all other Unix platforms, but it probably deserves a mention in the documentation when Linux is the most common platform on which coreutils is used. I should submit a patch.