New Sysd
Presentation
As the Systemd now replaces SysVinit, it is time to get familiar with it and learn new commands.
Systemd is quicker because it uses fewer scripts and tries to run more tasks in parallel (Systemdcalls them units).
The global Systemd configuration is stored in the /etc/systemd directory. The service configuration files are located in the /usr/lib/systemd/system directory. Custom service configuration files are stored in the /etc/systemd/system directory.
Systemd is quicker because it uses fewer scripts and tries to run more tasks in parallel (Systemdcalls them units).
The global Systemd configuration is stored in the /etc/systemd directory. The service configuration files are located in the /usr/lib/systemd/system directory. Custom service configuration files are stored in the /etc/systemd/system directory.
To get the current release of Systemd, type:
# systemctl --version systemd 208 +PAM +LIBWRAP +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ
Boot process
Systemd primary task is to manage the boot process and provides informations about it.
To get the boot process duration, type:
To get the boot process duration, type:
# systemd-analyze Startup finished in 422ms (kernel) + 2.722s (initrd) + 9.674s (userspace) = 12.820s
To get the time spent by each task during the boot process, type:
# systemd-analyze blame 7.029s network.service 2.241s plymouth-start.service 1.293s kdump.service 1.156s plymouth-quit-wait.service 1.048s firewalld.service 632ms postfix.service 621ms tuned.service 460ms iprupdate.service 446ms iprinit.service 344ms accounts-daemon.service ... 7ms systemd-update-utmp-runlevel.service 5ms systemd-random-seed.service 5ms sys-kernel-config.mount
To get the list of the critical chain of tasks during the boot process (any additional delay of these tasks would cause an increase of the overall boot time), type:
# systemd-analyze critical-chain
The time after the unit is active or started is printed after the "@" character.
The time the unit takes to start is printed after the "+" character.
multi-user.target @6.167s
└─mariadb.service @2.661s +3.505s
└─network.target @2.649s
└─network.service @2.168s +478ms
└─NetworkManager.service @1.993s +174ms
└─firewalld.service @826ms +1.162s
└─basic.target @822ms
└─sockets.target @821ms
└─dbus.socket @820ms
└─sysinit.target @813ms
└─systemd-update-utmp.service @806ms +6ms
└─auditd.service @747ms +58ms
└─local-fs.target @742ms
└─boot.mount @709ms +32ms
└─systemd-fsck@dev-disk-by\x2duuid-497a43ab\x2d33b0\x2
└─dev-disk-by\x2duuid-497a43ab\x2d33b0\x2d4153\x2d9f
To get the list of the critical chain for a particular service (here firewalld), type:
# systemd-analyze critical-chain firewalld.service
The time after the unit is active or started is printed after the "@" character.
The time the unit takes to start is printed after the "+" character.
firewalld.service +1.162s
└─basic.target @822ms
└─sockets.target @821ms
└─dbus.socket @820ms
└─sysinit.target @813ms
└─systemd-update-utmp.service @806ms +6ms
└─auditd.service @747ms +58ms
└─local-fs.target @742ms
└─boot.mount @709ms +32ms
└─systemd-fsck@dev-disk-by\x2duuid-497a43ab\x2d33b0\x2d4153\x2d9
└─dev-disk-by\x2duuid-497a43ab\x2d33b0\x2d4153\x2d9f8d\x2d7788
To get the list of the critical chain for a particular target (here basic.target), type:
# systemd-analyze critical-chain basic.target | grep target
basic.target @822ms
└─sockets.target @821ms
└─sysinit.target @813ms
└─local-fs.target @742ms
To get the list of the dependencies, type:
# systemctl list-dependencies default.target ├─abrt-ccpp.service ├─abrt-oops.service ... ├─tuned.service ├─basic.target │ ├─firewalld.service │ ├─microcode.service ... ├─getty.target │ ├─getty@tty1.service │ └─serial-getty@ttyS0.service └─remote-fs.target
To get the list of dependencies for a particular service (here sshd), type:
# systemctl list-dependencies sshd.service
To get the list of dependencies for a particular target (here graphical.target), type:
# systemctl list-dependencies graphical.target | grep target graphical.target └─multi-user.target ├─basic.target │ ├─paths.target │ ├─slices.target │ ├─sockets.target │ ├─sysinit.target │ │ ├─cryptsetup.target │ │ ├─local-fs.target │ │ └─swap.target │ └─timers.target ├─getty.target └─remote-fs.target
You can find additional information on this point in the Lennart Poettering’s blog.
In case you get boot problems, the Systemd debugging page may also help you.
In case you get boot problems, the Systemd debugging page may also help you.
Journal analysis
In addition, Systemd handles the system event log through Journald. The rsyslogd daemon, although present by default, is not mandatory any more.
To get the content of the Systemd journal, type:
# journalctl
To get all the events related to the crond process in the journal, type:
# journalctl /sbin/crond
Note: You can replace /sbin/crond by `which crond`.
To get all the events since the last boot, type:
# journalctl -b
To get all the events that appeared today in the journal, type:
# journalctl --since=today
To get all the events with a syslog priority of err, type:
# journalctl -p err
To get the 10 last events and wait for any new one (like “tail -f /var/log/messages“), type:
# journalctl -f
By default, Journald logs are stored in the /run/log/journal directory and disappear after a reboot.
To store Journald logs in a more permanent way, type:
To store Journald logs in a more permanent way, type:
# mkdir /var/log/journal # echo "SystemMaxUse=50M" >>/etc/systemd/journald.conf# systemctl restart systemd-journald
Note: Setting the SystemMaxUse variable is necessary because otherwise 10% of the filesystem where the /var/log/journal is stored may be used at maximum by the journal. Besides the space used, this will slow down the boot process and potentially the whole system (see details here).
Additional information about Journald is available in the Lennart Poettering’s blog or Lennart Poettering’s video (44min: the first ten minutes are very interesting concerning security issues).
Control groups
Systemd organizes tasks in control groups. For example, all the processes started by an apachewebserver will be in the same control group, CGI scripts included.
To get the full hierarchy of control groups, type:
# systemd-cgls ├─user.slice │ └─user-1000.slice │ └─session-1.scope │ ├─2889 gdm-session-worker [pam/gdm-password] │ ├─2899 /usr/bin/gnome-keyring-daemon --daemonize --login │ ├─2901 gnome-session --session gnome-classic . . └─iprupdate.service └─785 /sbin/iprupdate --daemon
To get the list of control group ordered by CPU, memory and disk I/O load, type:
# systemd-cgtop Path Tasks %CPU Memory Input/s Output/s / 213 3.9 829.7M - - /system.slice 1 - - - - /system.slice/ModemManager.service 1 - - - -
To kill all the processes associated with an apache server (CGI scripts included), type:
# systemctl kill httpd
To put resource limits on a service (here 500 CPUShares), type:
# systemctl set-property httpd.service CPUShares=500
Note1: The change is written into the service unit file. Use the –runtime option to avoid this behavior.
Note2: By default, each service owns 1024 CPUShares. Nothing prevents you from giving a value smaller or bigger.
Note2: By default, each service owns 1024 CPUShares. Nothing prevents you from giving a value smaller or bigger.
To get the current CPUShares service value, type:
# systemctl show -p CPUShares httpd.service CPUShares=500
Or:
# systemctl show httpd.service | grep CPUShares CPUShares=500
Note: Each time a resource limit is set on a service, a directory of the same name with the .dsuffix is created in /etc/systemd/system. For example, in the previous case, a directory named/etc/systemd/system/httpd.service.d is created with a file called 90-CPUShares.conf in it and the following content:
[Service] CPUShares=500
Note: The newly created directory (here /etc/systemd/system/httpd.service.d) can also be used to customize the service configuration file.
On this topic, you can additionally watch Georgios’ Magklaras demo (24min).
Also, if you need to use RT (Real-Time) services, be ready to apply additional RT configurations.
Also, if you need to use RT (Real-Time) services, be ready to apply additional RT configurations.
Service management
Systemd deals with all the aspects of the service management. The systemctl command replaces the chkconfig and the service commands. The old commands are now a link to thesystemctl command.
To activate the NTP service at boot, type:
# systemctl enable ntpd
Note1: You should specify ntpd.service but by default the .service suffix will be added.
Note2: If you specify a path, the .mount suffix will be added.
Note3: If you mention a device, the .device suffix will be added.
Note2: If you specify a path, the .mount suffix will be added.
Note3: If you mention a device, the .device suffix will be added.
To deactivate it, start it, stop it, restart it, reload it, type:
# systemctl disable ntpd # systemctl start ntpd # systemctl stop ntpd # systemctl restart ntpd # systemctl reload ntpd
Note1: The reload option is not available for all the services.
Note2: It is also possible to mask and unmask a service. Masking a service prevents it from being started manually, by another service or by D-Bus.
Note2: It is also possible to mask and unmask a service. Masking a service prevents it from being started manually, by another service or by D-Bus.
To know if the NTP service is activated at boot, type:
# systemctl is-enabled ntpd enabled
To know if the NTP service is running, type:
# systemctl is-active ntpd inactive
To get the status of the Apache service, type:
# systemctl status httpd httpd.service - The Apache HTTP Server Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled) Active: active (running) since Tue 2014-08-21 11:48:23 CEST; 44s ago Main PID: 2446 (httpd) Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec" CGroup: /system.slice/httpd.service └─2446 /usr/sbin/httpd -DFOREGROUND └─2447 /usr/sbin/httpd -DFOREGROUND └─2448 /usr/sbin/httpd -DFOREGROUND └─2449 /usr/sbin/httpd -DFOREGROUND └─2450 /usr/sbin/httpd -DFOREGROUND └─2451 /usr/sbin/httpd -DFOREGROUND └─2452 /usr/sbin/httpd -DFOREGROUND Aug 21 11:48:23 server.example.com systemd[1]: Starting The Apache HTTP Ser.... Aug 21 11:48:23 server.example.com systemd[1]: Started The Apache HTTP Server. Hint: Some lines were ellipsized, use -l to show in full.
Note1: In the line starting with “Loaded:”, you learn that the unit configuration file named/usr/lib/systemd/system/httpd.service has been loaded by Systemd. You also learn that the service isn’t started at boot time (disabled).
Note2: In the line beginning by “Active:”, you are informed that the service has been started for 44 seconds and is thus currently running (active).
Note3: The “Status:” line is specific to the Apache service and gives you a quick report of the service activity.
Note4: The line starting with “CGroup:” gives you all the information about the CGroup that theApache service is part of (here /system.slice/httpd.service).
Note2: In the line beginning by “Active:”, you are informed that the service has been started for 44 seconds and is thus currently running (active).
Note3: The “Status:” line is specific to the Apache service and gives you a quick report of the service activity.
Note4: The line starting with “CGroup:” gives you all the information about the CGroup that theApache service is part of (here /system.slice/httpd.service).
If you change a service configuration, you will need to reload it:
# systemctl daemon-reload
Note: The systemd-delta command displays the list of changes in the service configuration files.
To get the list of all the units (services, mount points, devices) with their status and description, type:
# systemctl
Note: You can use the arrow keys to move inside the unit list.
To get a more readable list, type:
# systemctl list-unit-files
To get the list of services that failed at boot, type:
# systemctl --failed
To get the status of a service (here httpd) on a remote server (here rhel7.example.com), type:
# systemctl -H root@rhel7.example.com status httpd.service
To get all the configuration details about a service (here httpd), type:
# systemctl show httpd Id=httpd.service Names=httpd.service Requires=basic.target Wants=system.slice Conflicts=shutdown.target Before=shutdown.target After=network.target remote-fs.target nss-lookup.target systemd-journald.socket Description=The Apache HTTP Server LoadState=loaded ActiveState=inactive ... ExecMainPID=0 ExecMainCode=0 ExecMainStatus=0
Digital Ocean provides an excellent article about Systemd unit files. In addition, the FedoraProjectwebsite can also help you if you need to write Systemd unit files.
Targets/Run levels
Systemd also deals with targets. A target is a grouping mechanism allowing several services to start at the same time. The list of services associated with a particular target is stored in a directory named with the target name and the suffix “.wants”. In some way, targets replace run levels but they are more general.
To move to maintenance mode, type:
# systemctl rescue
Note: There is also an emergency target only available when set up in the kernel boot line (systemd.unit=emergency.target) and for critical situations.
To move to the level 3 (equivalent to the previous level 3), type:
# systemctl isolate runlevel3.target
Or:
# systemctl isolate multi-user.target
To move to the graphical level (equivalent to the previous level 5), type:
# systemctl isolate graphical.target
To set the default run level to non-graphical mode, type:
# systemctl set-default multi-user.target
To set the default run level to graphical mode, type:
# systemctl set-default graphical.target
To get the current default run level, type:
# systemctl get-default graphical.target
To stop a server, type:
# systemctl poweroff
Note: You can still use the poweroff command, a link to the systemctl command has been created (the same thing is true for the halt and reboot commands).
To reboot a server, suspend it or put it into hibernation, type:
# systemctl reboot # systemctl suspend # systemctl hibernate
Linux standardization
Systemd‘s authors have decided to help Linux standardization among distributions. ThroughSystemd, changes happen in the localization of some configuration files.
Miscellaneous
To get the server hostnames, type:
# hostnamectl
Static hostname: rhel7.example.com
Icon name: computer-laptop
Chassis: laptop
Machine ID: bcdc71f1943f4d859aa37e54a422938d
Boot ID: f84556924b4e4bbf9c4a82fef4ac26d0
Operating System: Red Hat Enterprise Linux Everything 7.0 (Maipo)
CPE OS Name: cpe:/o:redhat:enterprise_linux:7.0:beta:everything
Kernel: Linux 3.10.0-54.0.1.el7.x86_64
Architecture: x86_64
Note: There are three kinds of hostnames: static, pretty, and transient.
“The static host name is the traditional hostname, which can be chosen by the user, and is stored in the /etc/hostname file. The transient hostname is a dynamic host name maintained by the kernel. It is initialized to the static host name by default, whose value defaults to localhost. It can be changed by DHCP or mDNS at runtime. The pretty hostname is a free-form UTF8 host name for presentation to the user.” Source: RHEL 7 Networking Guide.
“The static host name is the traditional hostname, which can be chosen by the user, and is stored in the /etc/hostname file. The transient hostname is a dynamic host name maintained by the kernel. It is initialized to the static host name by default, whose value defaults to localhost. It can be changed by DHCP or mDNS at runtime. The pretty hostname is a free-form UTF8 host name for presentation to the user.” Source: RHEL 7 Networking Guide.
To assign the rhel7 hostname permanently to the server, type:
# hostnamectl set-hostname rhel7
Note: With this syntax a
ll three hostnames (static, pretty, and transient) take the rhel7 value at the same time. However, it is possible to set the three hostnames separately by using the –pretty, –static, and –transient options.
To get the current locale, virtual console keymap and X11 layout, type:
# localectl System Locale: LANG=en_US.UTF-8 VC Keymap: en_US X11 Layout: en_US
To assign the en_GB.utf8 value to the locale, type:
# localectl set-locale LANG=en_GB.utf8
To assign the en_GB value to the virtual console keymap, type:
# localectl set-keymap en_GB
To assign the en_GB value to the X11 layout, type:
# localectl set-x11-keymap en_GB
To get the current date and time, type:
# timedatectl Local time: Fri 2014-01-24 22:34:05 CET Universal time: Fri 2014-01-24 21:34:05 UTC RTC time: Fri 2014-01-24 21:34:05 Timezone: Europe/Madrid (CET, +0100) NTP enabled: yes NTP synchronized: yes RTC in local TZ: no DST active: no Last DST change: DST ended at Sun 2013-10-27 02:59:59 CEST Sun 2013-10-27 02:00:00 CET Next DST change: DST begins (the clock jumps one hour forward) at Sun 2014-03-30 01:59:59 CET Sun 2014-03-30 03:00:00 CEST
To set the current date, type:
# timedatectl set-time YYYY-MM-DD
To set the current time, type:
# timedatectl set-time HH:MM:SS
To get the list of time zones, type:
# timedatectl list-timezones
To change the time zone to America/New_York, type:
# timedatectl set-timezone America/New_York
To get the users’ list, type:
# loginctl list-users UID USER 42 gdm 1000 tom 0 root
To get the list of all current user sessions, type:
# loginctl list-sessions SESSION UID USER SEAT 1 1000 tom seat0 1 sessions listed.
To get the properties of the user tom, type:
# loginctl show-user tom UID=1000 GID=1000 Name=tom Timestamp=Fri 2014-01-24 21:53:43 CET TimestampMonotonic=160754102 RuntimePath=/run/user/1000 Slice=user-1000.slice Display=1 State=active Sessions=1 IdleHint=no IdleSinceHint=0 IdleSinceHintMonotonic=0
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