Emanuele Rocca: systemd is your friend
Today I want to talk a bit about some cool features of systemd, the default Debian init system since the release of Jessie. Ubuntu has also adopted systemd in 15.04, meaning that you are going to find it literally everywhere.
Logging The component responsible for logging in systemd is called journal. It collects and stores logs in a structured, indexed journal (hence the name). The journal can replace traditional syslog daemons such as rsyslog and syslog-ng, or work together with them. By default Debian keeps on using rsyslog, but if you don't need to ship logs to a centralized server (or do other fancy things) it is possible to stop using rsyslog right now and rely on systemd-journal instead. The obvious question is: why would anybody use a binary format for logs instead of a bunch of tried and true plain-text files? As it turns out, there are quite a lot of good reasons to do so. The killer features of systemd-journald for me are:
- Index tons of logs while being able to search with good performance: O(log(n)) instead of O(n) which is what you get with text files
- No need to worry about log rotation anymore, in any shape or form
journalctl -b # Show all messages since last boot journalctl -f # Tail your logs journalctl --since=yesterday # Show all messages produced since yesterday journalctl -pcrit # Filter messages by priority journalctl /bin/su # Filter messages by program journalctl --disk-usage # The amount of space in use for journalingFurther reading:
Containers A relatively little known component of systemd is systemd-nspawn. It is a small, straightforward container manager. If you don't already have a chroot somewhere, here is how to create a basic Debian Jessie chroot under /srv/chroots/jessie:
$ debootstrap jessie /srv/chroots/jessie http://http.debian.net/debian/With systemd-nspawn you can easily run a shell inside the chroot:
$ sudo systemd-nspawn -D /srv/chroots/jessie Spawning container jessie on /srv/chroots/jessie. Press ^] three times within 1s to kill container. /etc/localtime is not a symlink, not updating container timezone. root@jessie:~#Done. Everything works out of the box: no need for you to mount /dev, /run and friends, systemd-nspawn took care of that. Networking also works. If you want to actually boot the system, just add the -b switch to the previous command:
$ sudo systemd-nspawn -b -D /srv/chroots/jessie Spawning container jessie on /srv/chroots/jessie. Press ^] three times within 1s to kill container. /etc/localtime is not a symlink, not updating container timezone. systemd 215 running in system mode. (+PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR) Detected virtualization 'systemd-nspawn'. Detected architecture 'x86-64'. Welcome to Debian GNU/Linux jessie/sid! Set hostname to <orion>. [ OK ] Reached target Remote File Systems (Pre). [ OK ] Reached target Encrypted Volumes. [ OK ] Reached target Paths. [ OK ] Reached target Swap. [ OK ] Created slice Root Slice. [ OK ] Created slice User and Session Slice. [ OK ] Listening on /dev/initctl Compatibility Named Pipe. [ OK ] Listening on Delayed Shutdown Socket. [ OK ] Listening on Journal Socket (/dev/log). [ OK ] Listening on Journal Socket. [ OK ] Created slice System Slice. [ OK ] Created slice system-getty.slice. [ OK ] Listening on Syslog Socket. Mounting POSIX Message Queue File System... Mounting Huge Pages File System... Mounting FUSE Control File System... Starting Copy rules generated while the root was ro... Starting Journal Service... [ OK ] Started Journal Service. [ OK ] Reached target Slices. Starting Remount Root and Kernel File Systems... [ OK ] Mounted Huge Pages File System. [ OK ] Mounted POSIX Message Queue File System. [ OK ] Mounted FUSE Control File System. [ OK ] Started Copy rules generated while the root was ro. [ OK ] Started Remount Root and Kernel File Systems. Starting Load/Save Random Seed... [ OK ] Reached target Local File Systems (Pre). [ OK ] Reached target Local File Systems. Starting Create Volatile Files and Directories... [ OK ] Reached target Remote File Systems. Starting Trigger Flushing of Journal to Persistent Storage... [ OK ] Started Load/Save Random Seed. Starting LSB: Raise network interfaces.... [ OK ] Started Create Volatile Files and Directories. Starting Update UTMP about System Boot/Shutdown... [ OK ] Started Trigger Flushing of Journal to Persistent Storage. [ OK ] Started Update UTMP about System Boot/Shutdown. [ OK ] Started LSB: Raise network interfaces.. [ OK ] Reached target Network. [ OK ] Reached target Network is Online. [ OK ] Reached target System Initialization. [ OK ] Listening on D-Bus System Message Bus Socket. [ OK ] Reached target Sockets. [ OK ] Reached target Timers. [ OK ] Reached target Basic System. Starting /etc/rc.local Compatibility... Starting Login Service... Starting LSB: Regular background program processing daemon... Starting D-Bus System Message Bus... [ OK ] Started D-Bus System Message Bus. Starting System Logging Service... [ OK ] Started System Logging Service. Starting Permit User Sessions... [ OK ] Started /etc/rc.local Compatibility. [ OK ] Started LSB: Regular background program processing daemon. Starting Cleanup of Temporary Directories... [ OK ] Started Permit User Sessions. Starting Console Getty... [ OK ] Started Console Getty. [ OK ] Reached target Login Prompts. [ OK ] Started Login Service. [ OK ] Reached target Multi-User System. [ OK ] Reached target Graphical Interface. Starting Update UTMP about System Runlevel Changes... [ OK ] Started Cleanup of Temporary Directories. [ OK ] Started Update UTMP about System Runlevel Changes. Debian GNU/Linux jessie/sid orion console orion login:That's it! Just one command to start a shell in your chroot or boot the container, again zero configuration needed. Finally, systemd provides a command called machinectl that allows you to introspect and control your container:
$ sudo machinectl status jessie jessie Since: Wed 2015-10-07 11:22:56 CEST; 55min ago Leader: 32468 (systemd) Service: nspawn; class container Root: /srv/chroots/jessie Address: fe80::8e70:5aff:fe81:2290 192.168.122.1 192.168.1.13 OS: Debian GNU/Linux jessie/sid Unit: machine-jessie.scope 32468 /lib/systemd/systemd system.slice dbus.service 32534 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile -... cron.service 32539 /usr/sbin/cron systemd-journald.service 32487 /lib/systemd/systemd-journald systemd-logind.service 32532 /lib/systemd/systemd-logind console-getty.service 32544 /sbin/agetty --noclear --keep-baud console 115200 38400 9600 vt102 rsyslog.service 32540 /usr/sbin/rsyslogd -nWith machinectl you can also reboot, poweroff, terminate your containers and more. There are so many things to learn about systemd and containers! Here are some references.