Difference between revisions of "Systemd"
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* If you do not specify the suffix, systemctl will assume ''.service''. For example, {{ic|netcfg}} and {{ic|netcfg.service}} are equivalent. | * If you do not specify the suffix, systemctl will assume ''.service''. For example, {{ic|netcfg}} and {{ic|netcfg.service}} are equivalent. | ||
− | * Mount points will automatically be translated into the appropriate ''.mount'' unit. For example, specifying {{ic|/home}} is equivalent to | + | * Mount points will automatically be translated into the appropriate ''.mount'' unit. For example, specifying {{ic|/home}} is equivalent to {{ic|home.mount}}. |
− | * Similiar to mount points, devices are automatically translated into the appropriate ''.device'' unit, therefore specifying {{ic|/dev/sda2}} is equivalent to | + | * Similiar to mount points, devices are automatically translated into the appropriate ''.device'' unit, therefore specifying {{ic|/dev/sda2}} is equivalent to {{ic|dev-sda2.device}}. |
See {{ic|man systemd.unit}} for details. | See {{ic|man systemd.unit}} for details. |
Revision as of 08:44, 20 July 2013
zh-CN:Systemd zh-TW:Systemd Template:Article summary start Template:Article summary text Template:Article summary heading Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary end From the project web page:
- systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. systemd provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux control groups, supports snapshotting and restoring of the system state, maintains mount and automount points and implements an elaborate transactional dependency-based service control logic.
Contents
- 1 Migration from SysVinit/initscripts
- 2 Basic systemctl usage
- 3 Running DMs under systemd
- 4 Native configuration
- 5 Writing custom .service files
- 6 Targets
- 7 Journal
- 8 Troubleshooting
- 9 See also
Migration from SysVinit/initscripts
- systemd and systemd-sysvcompat are both installed by default on installation media newer than 2012-10-13. This section is aimed at Arch Linux installations that still rely on sysvinit and initscripts.
- If you are running Arch Linux inside a VPS, please see Virtual Private Server#Moving your VPS from initscripts to systemd.
Considerations before switching
- Do some reading about systemd.
- Note the fact that systemd has a journal system that replaces syslog, although the two can co-exist. See #Journal.
- While systemd can replace some of the functionality of cron, acpid, or xinetd, there is no need to switch away from using the traditional daemons unless you want to.
- Interactive initscripts are not working with systemd. In particular, netcfg-menu cannot be used at system start-up (FS#31377).
Installation procedure
- Install systemd from the official repositories.
- Append the following to your kernel parameters:
init=/usr/lib/systemd/systemd
. - Once completed you may enable any desired services via the use of
systemctl enable service_name
(this roughly equates to what you included in theDAEMONS
array. New names can be found in Daemons List). - Reboot your system and verify that systemd is currently active by issuing the following command:
cat /proc/1/comm
. This should return the stringsystemd
. - Make sure your hostname is set correctly under systemd:
hostnamectl set-hostname myhostname
. - Proceed to remove initscripts and sysvinit from your system and install systemd-sysvcompat.
- Optionally, remove the
init=/usr/lib/systemd/systemd
parameter as it is no longer needed. systemd-sysvcompat provides the default init.
Supplementary information
- If you have
quiet
in your kernel parameters, you might want to remove it for your first couple of systemd boots, to assist with identifying any issues during boot.
- It is not necessary to add your user to groups (
sys
,disk
,lp
,network
,video
,audio
,optical
,storage
,scanner
,power
, etc.) for most use cases with systemd. The groups can even cause some functionality to break. For example, theaudio
group will break fast user switching and allows applications to block software mixing. Every PAM login provides a logind session, which for a local session will give you permissions via POSIX ACLs on audio/video devices, and allow certain operations like mounting removable storage via udisks.
- See the Network Configuration article for how to set up networking targets.
Basic systemctl usage
The main command used to introspect and control systemd is systemctl. Some of its uses are examining the system state and managing the system and services. See man 1 systemctl
for more details.
-H user@host
switch to control a systemd instance on a remote machine. This will use SSH to connect to the remote systemd instance.Analyzing the system state
List running units:
$ systemctl
or:
$ systemctl list-units
List failed units:
$ systemctl --failed
The available unit files can be seen in /usr/lib/systemd/system/
and /etc/systemd/system/
(the latter takes precedence). You can see a list of the installed unit files with:
$ systemctl list-unit-files
Using units
Units can be, for example, services (.service), mount points (.mount), devices (.device) or sockets (.socket).
When using systemctl, you generally have to specify the complete name of the unit file, including its suffix, for example sshd.socket. There are however a few short forms when specifying the unit in the following systemctl commands:
- If you do not specify the suffix, systemctl will assume .service. For example,
netcfg
andnetcfg.service
are equivalent. - Mount points will automatically be translated into the appropriate .mount unit. For example, specifying
/home
is equivalent tohome.mount
. - Similiar to mount points, devices are automatically translated into the appropriate .device unit, therefore specifying
/dev/sda2
is equivalent todev-sda2.device
.
See man systemd.unit
for details.
Activate a unit immediately:
# systemctl start unit
Deactivate a unit immediately:
# systemctl stop unit
Restart a unit:
# systemctl restart unit
Ask a unit to reload its configuration:
# systemctl reload unit
Show the status of a unit, including whether it is running or not:
$ systemctl status unit
Check whether a unit is already enabled or not:
$ systemctl is-enabled unit
Enable a unit to be started on bootup:
# systemctl enable unit
[Install]
section are usually called automatically by other services. If you need to install them manually, use the following command, replacing foo with the name of the service.
# ln -s /usr/lib/systemd/system/foo.service /etc/systemd/system/graphical.target.wants/
Disable a unit to not start during bootup:
# systemctl disable unit
Show the manual page associated with a unit (this has to be supported by the unit file):
$ systemctl help unit
Reload systemd, scanning for new or changed units:
# systemctl daemon-reload
Power management
polkit is necessary for power management. If you are in a local systemd-logind user session and no other session is active, the following commands will work without root privileges. If not (for example, because another user is logged into a tty), systemd will automatically ask you for the root password.
Shut down and reboot the system:
$ systemctl reboot
Shut down and power-off the system:
$ systemctl poweroff
Suspend the system:
$ systemctl suspend
Put the system into hibernation:
$ systemctl hibernate
Put the system into hybrid-sleep state (or suspend-to-both):
$ systemctl hybrid-sleep
Running DMs under systemd
To enable graphical login, run your preferred Display Manager daemon (e.g. KDM). At the moment, service files exist for GDM, KDM, SLiM, XDM, LXDM, LightDM, and SDDMAUR.
# systemctl enable kdm
This should work out of the box. If not, you might have a default.target set manually or from an older install:
# ls -l /etc/systemd/system/default.target
/etc/systemd/system/default.target -> /usr/lib/systemd/system/graphical.target
Simply delete the symlink and systemd will use its stock default.target (i.e. graphical.target).
# rm /etc/systemd/system/default.target
Using systemd-logind
In order to check the status of your user session, you can use loginctl
. All PolicyKit actions like suspending the system or mounting external drives will work out of the box.
$ loginctl show-session $XDG_SESSION_ID
Native configuration
644
permissions and root:root
ownership.Virtual console
The virtual console (keyboard mapping, console font and console map) is configured in /etc/vconsole.conf
or by using the localectl tool.
For more information, see console fonts and keymaps.
Hardware clock
systemd will use UTC for the hardware clock by default.
Hardware clock in localtime
If you want to change the hardware clock to use local time (strongly discouraged) do:
# timedatectl set-local-rtc true
If you want to revert to the hardware clock being in UTC, do:
# timedatectl set-local-rtc false
Be warned that, if the hardware clock is set to localtime, dealing with daylight saving time is messy. If the DST changes when your computer is off, your clock will be wrong on next boot (there is a lot more to it). Recent kernels set the system time from the RTC directly on boot, assuming that the RTC is in UTC. This means that if the RTC is in local time, then the system time will first be set up wrongly and then corrected shortly afterwards on every boot. This is the root of certain weird bugs (time going backwards is rarely a good thing).
One reason for allowing the RTC to be in local time is to allow dual boot with Windows (which uses localtime). However, Windows is able to deal with the RTC being in UTC with a simple registry fix. It is recommended to configure Windows to use UTC, rather than Linux to use localtime. If you make Windows use UTC, also remember to disable the "Internet Time Update" Windows feature, so that Windows does not mess with the hardware clock, trying to sync it with internet time. You should instead leave touching the RTC and syncing it to internet time to Linux, by enabling an NTP daemon, as suggested previously.
For more information, see Time.
Kernel modules
See Kernel modules#Configuration.
Filesystem mounts
The default setup will automatically fsck and mount filesystems before starting services that need them to be mounted. For example, systemd automatically makes sure that remote filesystem mounts like NFS or Samba are only started after the network has been set up. Therefore, local and remote filesystem mounts specified in /etc/fstab
should work out of the box.
See man 5 systemd.mount
for details.
Automount
If you have a large /home
partition, it might be better to allow services that do not depend on /home
to start while /home
is checked by fsck. This can be achieved by adding the following options to the /etc/fstab
entry of your /home
partition:
noauto,x-systemd.automount
This will fsck and mount /home
when it is first accessed, and the kernel will buffer all file access to /home
until it is ready.
/home
filesystem type autofs
, which is ignored by mlocate by default. The speedup of automounting /home
may not be more than a second or two, depending on your system, so this trick may not be worth it.The same applies to remote filesystem mounts. If you want them to be mounted only upon access, you will need to use the noauto,x-systemd.automount
parameters. In addition, you can use the x-systemd.device-timeout=#
option to specify a timeout in case the network resource is not available.
If you have encrypted filesystems with keyfiles, you can also add the noauto
parameter to the corresponding entries in /etc/crypttab
. systemd will then not open the encrypted device on boot, but instead wait until it is actually accessed and then automatically open it with the specified keyfile before mounting it. This might save a few seconds on boot if you are using an encrypted RAID device for example, because systemd does not have to wait for the device to become available. For example:
/etc/crypttab
data /dev/md0 /root/key noauto
LVM
If you have LVM volumes not activated via the initramfs, enable the lvm-monitoring service, which is provided by the lvm2 package.
ACPI power management
systemd handles some power-related ACPI events. They can be configured via the following options from /etc/systemd/logind.conf
:
HandlePowerKey
: specifies which action is invoked when the power key is pressed.HandleSuspendKey
: specifies which action is invoked when the suspend key is pressed.HandleHibernateKey
: specifies which action is invoked when the hibernate key is pressed.HandleLidSwitch
: specifies which action is invoked when the lid is closed.
The specified action can be one of ignore
, poweroff
, reboot
, halt
, suspend
, hibernate
, hybrid-sleep
, lock
or kexec
.
If these options are not configured, systemd will use its defaults: HandlePowerKey=poweroff
, HandleSuspendKey=suspend
, HandleHibernateKey=hibernate
, and HandleLidSwitch=suspend
.
On systems which run no graphical setup or only a simple window manager like i3 or awesome, this may replace the acpid daemon which is usually used to react to these ACPI events.
- Run
systemctl restart systemd-logind
for your changes to take effect. - systemd cannot handle AC and Battery ACPI events, so if you use Laptop Mode Tools or other similar tools acpid is still required.
In the current version of systemd, the Handle*
options will apply throughout the system unless they are "inhibited" (temporarily turned off) by a program, such as a power manager inside a desktop environment. If these inhibits are not taken, you can end up with a situation where systemd suspends your system, then when it wakes up the other power manager suspends it again.
Handle
options to ignore
if you want your ACPI events to be handled by Xfce, acpid or other programs.For systemctl hibernate
to work on your system you need to follow the instructions at Pm-utils#Hibernation (suspend2disk) and possibly at Pm-utils#Mkinitcpio Resume Hook (pm-utils does not need to be installed).
Sleep hooks
systemd does not use pm-utils to put the machine to sleep when using systemctl suspend
, systemctl hibernate
or systemctl hybrid-sleep
; pm-utils hooks, including any custom hooks, will not be run. However, systemd provides two similar mechanisms to run custom scripts on these events.
Suspend/resume service files
Service files can be hooked into suspend.target, hibernate.target and sleep.target to execute actions before or after suspend/hibernate. Separate files should be created for user actions and root/system actions. To activate the user service files run systemctl enable suspend@user && systemctl enable resume@user
. Examples:
/etc/systemd/system/suspend@.service
[Unit] Description=User suspend actions Before=sleep.target [Service] User=%I Type=forking Environment=DISPLAY=:0 ExecStartPre= -/usr/bin/pkill -u %u unison ; /usr/local/bin/music.sh stop ; /usr/bin/mysql -e 'slave stop' ExecStart=/usr/bin/sflock [Install] WantedBy=sleep.target
/etc/systemd/system/resume@.service
[Unit] Description=User resume actions After=suspend.target [Service] User=%I Type=simple ExecStartPre=/usr/local/bin/ssh-connect.sh ExecStart=/usr/bin/mysql -e 'slave start' [Install] WantedBy=suspend.target
For root/system actions (activate with systemctl enable root-suspend
):
/etc/systemd/system/root-resume.service
[Unit] Description=Local system resume actions After=suspend.target [Service] Type=simple ExecStart=/usr/bin/systemctl restart mnt-media.automount [Install] WantedBy=suspend.target
/etc/systemd/system/root-suspend.service
[Unit] Description=Local system suspend actions Before=sleep.target [Service] Type=simple ExecStart=-/usr/bin/pkill sshfs [Install] WantedBy=sleep.target
A couple of handy hints about these service files (more in man systemd.service
):
- If
Type=OneShot
then you can use multipleExecStart=
lines. Otherwise only oneExecStart
line is allowed. You can add more commands with eitherExecStartPre
or by separating commands with a semicolon (see the first example above; note the spaces before and after the semicolon, as they are required). - A command prefixed with
-
will cause a non-zero exit status to be ignored and treated as a successful command. - The best place to find errors when troubleshooting these service files is of course with journalctl.
Combined Suspend/resume service file
With the combined suspend/resume service file, a single hook does all the work for different phases (sleep/resume) and for different targets (suspend/hibernate/hybrid-sleep).
Example and explanation:
/etc/systemd/system/wicd-sleep.service
[Unit] Description=Wicd sleep hook Before=sleep.target StopWhenUnneeded=yes [Service] Type=oneshot RemainAfterExit=yes ExecStart=-/usr/share/wicd/daemon/suspend.py ExecStop=-/usr/share/wicd/daemon/autoconnect.py [Install] WantedBy=sleep.target
RemainAfterExit=yes
: After started, the service is considered active until it is explicitly stopped.StopWhenUnneeded=yes
: When active, the service will be stopped if no other active service requires it. In this specific example, it will be stopped after sleep.target is stopped.- Because sleep.target is pulled in by suspend.target, hibernate.target and hybrid-sleep.target and sleep.target itself is a StopWhenUnneeded service, the hook is guaranteed to start/stop properly for different tasks.
Hooks in /usr/lib/systemd/system-sleep
systemd runs all executables in /usr/lib/systemd/system-sleep/
, passing two arguments to each of them:
- Argument 1: either
pre
orpost
, depending on whether the machine is going to sleep or waking up - Argument 2:
suspend
,hibernate
orhybrid-sleep
, depending on which is being invoked
In contrast to pm-utils, systemd will run these scripts concurrently and not one after another.
The output of any custom script will be logged by systemd-suspend.service, systemd-hibernate.service or systemd-hybrid-sleep.service. You can see its output in systemd's journal:
# journalctl -b -u systemd-suspend
An example of a custom sleep script:
/usr/lib/systemd/system-sleep/example.sh
#!/bin/sh case $1/$2 in pre/*) echo "Going to $2..." ;; post/*) echo "Waking up from $2..." ;; esac
Do not forget to make your script executable:
# chmod a+x /usr/lib/systemd/system-sleep/example.sh
See man 7 systemd.special
and man 8 systemd-sleep
for more details.
Temporary files
systemd-tmpfiles uses configuration files in /usr/lib/tmpfiles.d/
and /etc/tmpfiles.d/
to describe the creation, cleaning and removal of volatile and temporary files and directories which usually reside in directories such as /run
or /tmp
. Each configuration file is named in the style of /etc/tmpfiles.d/program.conf
. This will also override any files in /usr/lib/tmpfiles.d/
with the same name.
tmpfiles are usually provided together with service files to create directories which are expected to exist by certain daemons. For example the Samba daemon expects the directory /run/samba
to exist and to have the correct permissions. The corresponding tmpfile looks like this:
/usr/lib/tmpfiles.d/samba.conf
D /run/samba 0755 root root
tmpfiles may also be used to write values into certain files on boot. For example, if you use /etc/rc.local
to disable wakeup from USB devices with echo USBE > /proc/acpi/wakeup
, you may use the following tmpfile instead:
/etc/tmpfiles.d/disable-usb-wake.conf
w /proc/acpi/wakeup - - - - USBE
See man 5 tmpfiles.d
for details.
/sys
since the systemd-tmpfiles-setup service may run before the appropriate device modules is loaded. In this case you could check whether the module has a parameter for the option you want to set with modinfo module
and set this option with a config file in /etc/modprobe.d. Otherwise you will have to write a udev rule to set the appropriate attribute as soon as the device appears.Units
A unit configuration file encodes information about a service, a socket, a device, a mount point, an automount point, a swap file or partition, a start-up target, a file system path or a timer controlled and supervised by systemd. The syntax is inspired by XDG Desktop Entry Specification .desktop files, which are in turn inspired by Microsoft Windows .ini files.
See man 5 systemd.unit
for details.
Writing custom .service files
See also systemd/Services.
Handling dependencies
With systemd, dependencies can be resolved by designing the unit files correctly. The most typical case is that the unit A requires the unit B to be running before A is started. In that case add Requires=B
and After=B
to the [Unit]
section of A. If the dependency is optional, add Wants=B
and After=B
instead. Note that Wants=
and Requires=
do not imply After=
, meaning that if After=
is not specified, the two units will be started in parallel.
Dependencies are typically placed on services and not on targets. For example, network.target is pulled in by whatever service configures your network interfaces, therefore ordering your custom unit after it is sufficient since network.target is started anyway.
Type
There are several different start-up types to consider when writing a custom service file. This is set with the Type=
parameter in the [Service]
section. See man systemd.service
for a more detailed explanation.
Type=simple
(default): systemd considers the service to be started up immediately. The process must not fork. Do not use this type if other services need to be ordered on this service, unless it is socket activated.Type=forking
: systemd considers the service started up once the process forks and the parent has exited. For classic daemons use this type unless you know that it is not necessary. You should specifyPIDFile=
as well so systemd can keep track of the main process.Type=oneshot
: this is useful for scripts that do a single job and then exit. You may want to setRemainAfterExit=yes
as well so that systemd still considers the service as active after the process has exited.Type=notify
: identical toType=simple
, but with the stipulation that the daemon will send a signal to systemd when it is ready. The reference implementation for this notification is provided by libsystemd-daemon.so.Type=dbus
: the service is considered ready when the specifiedBusName
appears on DBus's system bus.
Editing provided unit files
To edit a unit file provided by a package, you can create a directory called /etc/systemd/system/unit.d/
for example /etc/systemd/system/httpd.service.d/
and place *.conf files in there to override or add new options. systemd will parse these *.conf files and apply them on top of the original unit. For example, if you simply want to add an additional dependency to a unit, you may create the following file:
/etc/systemd/system/unit.d/customdependency.conf
[Unit] Requires=new dependency After=new dependency
Then run the following for your changes to take effect:
# systemctl daemon-reload # systemctl restart unit
Alternatively you can copy the old unit file from /usr/lib/systemd/system/
to /etc/systemd/system/
and make your changes there. A unit file in /etc/systemd/system/
always overrides the same unit in /usr/lib/systemd/system/
. Note that when the original unit in /usr/lib/
is changed due to a package upgrade, these changes will not automatically apply to your custom unit file in /etc/
. Additionally you will have to manually reenable the unit with systemctl reenable unit
. It is therefore recommended to use the *.conf method described before instead.
As the provided unit files will be updated from time to time, use systemd-delta for system maintenance.
Syntax highlighting for units within Vim
Syntax highlighting for systemd unit files within Vim can be enabled by installing vim-systemd from the official repositories.
Targets
systemd uses targets which serve a similar purpose as runlevels but act a little different. Each target is named instead of numbered and is intended to serve a specific purpose with the possibility of having multiple ones active at the same time. Some targets are implemented by inheriting all of the services of another target and adding additional services to it. There are systemd targets that mimic the common SystemVinit runlevels so you can still switch targets using the familiar telinit RUNLEVEL
command.
Get current targets
The following should be used under systemd instead of running runlevel
:
$ systemctl list-units --type=target
Create custom target
The runlevels that are assigned a specific purpose on vanilla Fedora installs; 0, 1, 3, 5, and 6; have a 1:1 mapping with a specific systemd target. Unfortunately, there is no good way to do the same for the user-defined runlevels like 2 and 4. If you make use of those it is suggested that you make a new named systemd target as /etc/systemd/system/your target
that takes one of the existing runlevels as a base (you can look at /usr/lib/systemd/system/graphical.target
as an example), make a directory /etc/systemd/system/your target.wants
, and then symlink the additional services from /usr/lib/systemd/system/
that you wish to enable.
Targets table
SysV Runlevel | systemd Target | Notes |
---|---|---|
0 | runlevel0.target, poweroff.target | Halt the system. |
1, s, single | runlevel1.target, rescue.target | Single user mode. |
2, 4 | runlevel2.target, runlevel4.target, multi-user.target | User-defined/Site-specific runlevels. By default, identical to 3. |
3 | runlevel3.target, multi-user.target | Multi-user, non-graphical. Users can usually login via multiple consoles or via the network. |
5 | runlevel5.target, graphical.target | Multi-user, graphical. Usually has all the services of runlevel 3 plus a graphical login. |
6 | runlevel6.target, reboot.target | Reboot |
emergency | emergency.target | Emergency shell |
Change current target
In systemd targets are exposed via target units. You can change them like this:
# systemctl isolate graphical.target
This will only change the current target, and has no effect on the next boot. This is equivalent to commands such as telinit 3
or telinit 5
in Sysvinit.
Change default target to boot into
The standard target is default.target, which is aliased by default to graphical.target (which roughly corresponds to the old runlevel 5). To change the default target at boot-time, append one of the following kernel parameters to your bootloader:
systemd.unit=multi-user.target
(which roughly corresponds to the old runlevel 3),systemd.unit=rescue.target
(which roughly corresponds to the old runlevel 1).
Alternatively, you may leave the bootloader alone and change default.target. This can be done using systemctl:
# systemctl enable multi-user.target
The effect of this command is output by systemctl; a symlink to the new default target is made at /etc/systemd/system/default.target
. This works if, and only if:
[Install] Alias=default.target
is in the target's configuration file. Currently, multi-user.target and graphical.target both have it.
Journal
systemd has its own logging system called the journal; therefore, running a syslog daemon is no longer required. To read the log, use:
# journalctl
By default (when Storage=
is set to auto
in /etc/systemd/journald.conf
), the journal writes to /var/log/journal/
. The directory /var/log/journal/
is a part of the systemd package. If you or some program delete that directory, systemd will not recreate it automatically; however, it will be recreated during the next update of the systemd package. Until then, logs will be written to /run/systemd/journal
, and logs will be lost on reboot.
Filtering output
journalctl allows you to filter the output by specific fields.
Examples:
Show all messages from this boot:
# journalctl -b
However, often one is interested in messages not from the current, but from the previous boot (e.g. if an unrecoverable system crash happened). Currently, this feature is not implemented, though there was a discussion at systemd-devel@lists.freedesktop.org (September/October 2012).
As a workaround you can use at the moment:
# journalctl --since=today | tac | sed -n '/-- Reboot --/{n;:r;/-- Reboot --/q;p;n;b r}' | tac
provided, that the previous boot happened today. Be aware that, if there are many messages for the current day, the output of this command can be delayed for quite some time.
Follow new messages:
# journalctl -f
Show all messages by a specific executable:
# journalctl /usr/lib/systemd/systemd
Show all messages by a specific process:
# journalctl _PID=1
Show all messages by a specific unit:
# journalctl -u netcfg
See man 1 journalctl
, man 7 systemd.journal-fields
, or Lennert's blog post for details.
Journal size limit
If the journal is persistent (non-volatile), its size limit is set to a default value of 10% of the size of the respective file system. For example, with /var/log/journal
located on a 50 GiB root partition this would lead to 5 GiB of journal data. The maximum size of the persistent journal can be controlled by SystemMaxUse
in /etc/systemd/journald.conf
, so to limit it for example to 50 MiB uncomment and edit the corresponding line to:
SystemMaxUse=50M
Refer to man journald.conf
for more info.
Journald in conjunction with syslog
Compatibility with classic syslog implementations is provided via a socket /run/systemd/journal/syslog
, to which all messages are forwarded. To make the syslog daemon work with the journal, it has to bind to this socket instead of /dev/log
(official announcement). The syslog-ng package in the repositories automatically provides the necessary configuration.
# systemctl enable syslog-ng
A good journalctl tutorial is here.
Troubleshooting
Shutdown/reboot takes terribly long
If the shutdown process takes a very long time (or seems to freeze) most likely a service not exiting is to blame. systemd waits some time for each service to exit before trying to kill it. To find out if you are affected, see this article.
Short lived processes do not seem to log any output
If journalctl -u foounit
does not show any output for a short lived service, look at the PID instead. For example, if systemd-modules-load.service
fails, and systemctl status systemd-modules-load
shows that it ran as PID 123, then you might be able to see output in the journal for that PID, i.e. journalctl -b _PID=123
. Metadata fields for the journal such as _SYSTEMD_UNIT and _COMM are collected asynchronously and rely on the /proc
directory for the process existing. Fixing this requires fixing the kernel to provide this data via a socket connection, similar to SCM_CREDENTIALS.
Diagnosing boot problems
Boot with these parameters on the kernel command line:
systemd.log_level=debug systemd.log_target=kmsg log_buf_len=1M
Disabling application crash dumps journaling
To get back normal core dump files, edit the following file in order to overwrite the settings from /lib/sysctl.d/
:
/etc/sysctl.d/49-coredump.conf
kernel.core_pattern = core kernel.core_uses_pid = 0
Then run:
# /usr/lib/systemd/systemd-sysctl
As before, you also need to "unlimit" the core files size in the shell:
$ ulimit -c unlimited
See sysctl.d and the documentation for /proc/sys/kernel for more information.
See also
- Official web site
- Wikipedia article
- Manual pages
- systemd optimizations
- FAQ
- Tips and tricks
- systemd for Administrators (PDF)
- About systemd on Fedora Project
- How to debug systemd problems
- Two part introductory article in The H Open magazine.
- Lennart's blog story
- Status update
- Status update2
- Status update3
- Most recent summary
- Fedora's SysVinit to systemd cheatsheet