Linux systemd and systemctl tutorial
Greeting guys, In this tutorial we will talk about linux systemd and how to use and manage it using systemctl.
We will give brief introduction about systemd and its process id and will find using command pstree. Later in this tutorial we will see how to use systemctl commands to list services, to check whether service is enabled.disabled, started /stopped and will stop, start, enable/disable, restart and reload commands options. Come lets jump in
Systemd
Systemd is system and service manager for Linux OS and run as first process on boot (as PID 1). It initializes the system and manages user space services. Starts processes in parallel whereas init was starting process in serial. That means systemd is faster than init. For systemd every resource which is known to systemd and know how to operate and manage is unit. This is important object of systemd tool how to deal. Information about these units are stored in configuration files called unit files.
systemd has its own logging system known as journal. It replaces the syslog daemon from sysVinit by using command journalctl.
You can check the all boot messages use command journalctl –b
To follow the messages system logs use journalctl –f it is similar as tail –f. (do it yourself)
[root@faraz ~]# journalctl - Logs begin at Thu 2016-02-25 13:21:59 PKT, end at Thu 2016-02-25 14:07:30 PKT. -- Feb 25 13:21:59 localhost.localdomain systemd-journal[89]: Runtime journal is using 6.2M (max allowed 49.6M, trying to leave 74.4M free of 490.2M available ? current limit 49.6M Feb 25 13:21:59 localhost.localdomain systemd-journal[89]: Runtime journal is using 6.2M (max allowed 49.6M, trying to leave 74.4M free of 490.2M available ? current limit 49.6M Feb 25 13:21:59 localhost.localdomain kernel: Initializing cgroup subsys cpuset Feb 25 13:21:59 localhost.localdomain kernel: Initializing cgroup subsys cpu Feb 25 13:21:59 localhost.localdomain kernel: Initializing cgroup subsys cpuacct Feb 25 13:21:59 localhost.localdomain kernel: Linux version 3.10.0-327.el7.x86_64 ([email protected]) (gcc version 4.8.3 20140911 (Red Hat 4.8.3-9) (GCC) ) #1 SMP Feb 25 13:21:59 localhost.localdomain kernel: BIOS-e820: [mem 0x000000003fff0000-0x000000003fffffff] ACPI data Feb 25 13:21:59 localhost.localdomain kernel: BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved Feb 25 13:21:59 localhost.localdomain kernel: NX (Execute Disable) protection: active x00000fff] usable ==> reserved Feb 25 14:06:05 faraz.test.server systemd[1]: Starting Location Lookup Service... Feb 25 14:06:05 faraz.test.server dbus[17211]: [system] Successfully activated service 'org.freedesktop.GeoClue2' Feb 25 14:06:05 faraz.test.server dbus-daemon[17211]: dbus[17211]: [system] Successfully activated service 'org.freedesktop.GeoClue2' Feb 25 14:06:05 faraz.test.server systemd[1]: Started Location Lookup Service. Feb 25 14:06:05 faraz.test.server polkitd[17273]: Registered Authentication Agent for unix-session:12 (system bus name :1.62 [/usr/bin/gnome-shell], object path /org/freedesktop Feb 25 14:06:06 faraz.test.server systemd-logind[17246]: Removed session c1. Feb 25 14:06:06 faraz.test.server systemd[1]: Removed slice user-42.slice. Feb 25 14:06:06 faraz.test.server systemd[1]: Stopping user-42.slice. Feb 25 14:06:10 faraz.test.server gnome-session[18924]: vmware-user: could not open /proc/fs/vmblock/dev Feb 25 14:06:11 faraz.test.server gnome-session[18924]: Entering running state
Pstree
Command pstree display the all process in tree form. As you can see PID for systemd is 1.
[root@faraz ~]# pstree
systemd---ModemManager---2*[{ModemManager}]
+-NetworkManager---dhclient
¦ +-2*[{NetworkManager}]
+-abrt-dbus---{abrt-dbus}
+-2*[abrt-watch-log]
+-abrtd
+-accounts-daemon---2*[{accounts-daemon}]
+-alsactl
+-at-spi-bus-laun---dbus-daemon---{dbus-daemon}
¦ +-3*[{at-spi-bus-laun}]
+-at-spi2-registr---{at-spi2-registr}
+-atd
+-auditd---audispd---sedispatch
¦ ¦ +-{audispd}
¦ +-{auditd}
+-avahi-daemon---avahi-daemon
+-bluetoothd
+-caribou---2*[{caribou}]
+-colord---2*[{colord}]
Systemctl
Systemctl is to control the state of systemd system and service manager. You can control your system with this command.
List all the units by using command systemctl or systemctl list-units both commands are working same.
[root@faraz ~]# systemctl UNIT LOAD ACTIVE SUB DESCRIPTION proc-sys-fs-binfmt_misc.automount loaded active running Arbitrary Executable File Formats File System Automount Point sys-devices-pci0000:00-0000:00:01.1-ata2-host1-target1:0:0-1:0:0:0-block-sr0.device loaded active plugged VBOX_CD-ROM sys-devices-pci0000:00-0000:00:03.0-net-enp0s3.device loaded active plugged 82540EM Gigabit Ethernet Controller (PRO/1000 MT Desktop Adapter) sys-devices-pci0000:00-0000:00:05.0-sound-card0.device loaded active plugged 82801AA AC'97 Audio Controller sys-devices-pci0000:00-0000:00:0d.0-ata3-host2-target2:0:0-2:0:0:0-block-sda-sda1.device loaded active plugged VBOX_HARDDISK 1 sys-devices-pci0000:00-0000:00:0d.0-ata3-host2-target2:0:0-2:0:0:0-block-sda-sda2.device loaded active plugged LVM PV CIG0oS-QFvE-vxjF-tHYG-Zz93-4Vvl-tSB6da on /dev/sda2 2 sys-devices-pci0000:00-0000:00:0d.0-ata3-host2-target2:0:0-2:0:0:0-block-sda.device loaded active plugged VBOX_HARDDISK sys-devices-platform-serial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS0 sys-devices-platform-serial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1 sys-devices-platform-serial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2 sys-devices-platform-serial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3
List all the failed units by using command systemctl –failed.
[root@faraz ~]# systemctl --failed UNIT LOAD ACTIVE SUB DESCRIPTION ? kdump.service loaded failed failed Crash recovery kernel arming ? rngd.service loaded failed failed Hardware RNG Entropy Gatherer Daemon ? xrdp-sesman.service loaded failed failed xrdp session manager ? xrdp.service loaded failed failed xrdp daemon LOAD = Reflects whether the unit definition was properly loaded. ACTIVE = The high-level unit activation state, i.e. generalization of SUB. SUB = The low-level unit activation state, values depend on unit type. 4 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use command systemctl list-unit-files. (Do it yourself)
To check the all active/failed services by using command systemctl list-units –t service. You can manage services after checking which service is active and inactive.
[root@faraz ~]# systemctl list-units -t service UNIT LOAD ACTIVE SUB DESCRIPTION abrt-ccpp.service loaded active exited Install ABRT coredump hook abrt-oops.service loaded active running ABRT kernel log watcher abrt-xorg.service loaded active running ABRT Xorg log watcher abrtd.service loaded active running ABRT Automated Bug Reporting Tool accounts-daemon.service loaded active running Accounts Service alsa-state.service loaded active running Manage Sound Card State (restore and store) atd.service loaded active running Job spooling tools auditd.service loaded active running Security Auditing Service avahi-daemon.service loaded active running Avahi mDNS/DNS-SD Stack blk-availability.service loaded active exited Availability of block devices bluetooth.service loaded active running Bluetooth service colord.service loaded active running Manage, Install and Generate Color Profiles crond.service loaded active running Command Scheduler cups.service loaded active running CUPS Printing Service dbus.service loaded active running D-Bus System Message Bus firewalld.service loaded active running firewalld - dynamic firewall daemon gdm.service loaded active running GNOME Display Manager gssproxy.service loaded active running GSSAPI Proxy Daemon iscsi-shutdown.service loaded active exited Logout off all iSCSI sessions on shutdown ? kdump.service loaded failed failed Crash recovery kernel arming
Services in Linux Managed by systemctl
In previous version of linux services were managed by service command but in latest version it is done by systemctl instead of service.
Systemctl is powerful command because this command you can not only start/stop/restart/reload but you can also check list of services on/off similarly like chkconfig.
You can check status of service by option status , to start service use option start and to stop use option stop.
You can restart and reload service with restart/reload options. Below examples will show how to use these options with systemctl
[root@faraz ~]# systemctl status sshd ? sshd.service - OpenSSH server daemon Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled) Active: inactive (dead) since Thu 2016-02-25 13:44:14 PKT; 5s ago Docs: man:sshd(8) man:sshd_config(5) Process: 1124 ExecStart=/usr/sbin/sshd -D $OPTIONS (code=exited, status=0/SUCCESS) Main PID: 1124 (code=exited, status=0/SUCCESS) Feb 25 13:23:12 faraz.test.server systemd[1]: Started OpenSSH server daemon. Feb 25 13:23:12 faraz.test.server systemd[1]: Starting OpenSSH server daemon... Feb 25 13:23:15 faraz.test.server sshd[1124]: Server listening on 0.0.0.0 port 122. Feb 25 13:23:15 faraz.test.server sshd[1124]: Server listening on :: port 122. Feb 25 13:38:14 faraz.test.server sshd[13901]: Accepted password for root from 192.168.40.112 port 56866 ssh2 Feb 25 13:44:13 faraz.test.server systemd[1]: Stopping OpenSSH server daemon... Feb 25 13:44:14 faraz.test.server systemd[1]: Stopped OpenSSH server daemon. [root@faraz ~]#
[root@faraz ~]# systemctl start sshd [root@faraz ~]# systemctl status sshd ? sshd.service - OpenSSH server daemon Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled) Active: active (running) since Thu 2016-02-25 13:44:37 PKT; 2s ago Docs: man:sshd(8) man:sshd_config(5) Main PID: 14319 (sshd) CGroup: /system.slice/sshd.service +-14319 /usr/sbin/sshd -D Feb 25 13:44:37 faraz.test.server systemd[1]: Started OpenSSH server daemon. Feb 25 13:44:37 faraz.test.server systemd[1]: Starting OpenSSH server daemon... Feb 25 13:44:37 faraz.test.server sshd[14319]: Server listening on 0.0.0.0 port 122. Feb 25 13:44:37 faraz.test.server sshd[14319]: Server listening on :: port 122. [root@faraz ~]#
[root@faraz ~]# systemctl stop sshd [root@faraz ~]# systemctl status sshd ? sshd.service - OpenSSH server daemon Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled) Active: inactive (dead) since Thu 2016-02-25 13:44:54 PKT; 1s ago Docs: man:sshd(8) man:sshd_config(5) Process: 14319 ExecStart=/usr/sbin/sshd -D $OPTIONS (code=exited, status=0/SUCCESS) Main PID: 14319 (code=exited, status=0/SUCCESS) Feb 25 13:44:37 faraz.test.server systemd[1]: Started OpenSSH server daemon. Feb 25 13:44:37 faraz.test.server systemd[1]: Starting OpenSSH server daemon... Feb 25 13:44:37 faraz.test.server sshd[14319]: Server listening on 0.0.0.0 port 122. Feb 25 13:44:37 faraz.test.server sshd[14319]: Server listening on :: port 122. Feb 25 13:44:54 faraz.test.server systemd[1]: Stopping OpenSSH server daemon... Feb 25 13:44:54 faraz.test.server systemd[1]: Stopped OpenSSH server daemon. [root@faraz ~]#
[root@faraz ~]# systemctl restart sshd [root@faraz ~]# systemctl reload sshd [root@faraz ~]# systemctl status sshd ? sshd.service - OpenSSH server daemon Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled) Active: active (running) since Thu 2016-02-25 13:57:22 PKT; 21s ago Docs: man:sshd(8) man:sshd_config(5) Process: 15445 ExecReload=/bin/kill -HUP $MAINPID (code=exited, status=0/SUCCESS) Main PID: 15314 (sshd) CGroup: /system.slice/sshd.service +-15314 /usr/sbin/sshd -D Feb 25 13:57:22 faraz.test.server systemd[1]: Started OpenSSH server daemon. Feb 25 13:57:22 faraz.test.server systemd[1]: Starting OpenSSH server daemon... Feb 25 13:57:22 faraz.test.server sshd[15314]: Server listening on 0.0.0.0 port 122. Feb 25 13:57:22 faraz.test.server sshd[15314]: Server listening on :: port 122. Feb 25 13:57:27 faraz.test.server sshd[15314]: Received SIGHUP; restarting. Feb 25 13:57:27 faraz.test.server systemd[1]: Reloaded OpenSSH server daemon. Feb 25 13:57:28 faraz.test.server sshd[15314]: Server listening on 0.0.0.0 port 122. Feb 25 13:57:28 faraz.test.server sshd[15314]: Server listening on :: port 122. [root@faraz ~]#
Now we will use systemctl to enable service instead of using chkconfig
To make service run at boot time we can make service enabled
To check if service is enabled or disabled use option is-enabled.
Syntax systemctl option service-daeman-name.
[root@faraz ~]# systemctl is-enabled sshd disabled [root@faraz ~]#
To enable service use below command
[root@faraz ~]# systemctl enable sshd Created symlink from /etc/systemd/system/multi-user.target.wants/sshd.service to /usr/lib/systemd/system/sshd.service. [root@faraz ~]#
To disable service
[root@faraz ~]# systemctl disable sshd Removed symlink /etc/systemd/system/multi-user.target.wants/sshd.service. [root@faraz ~]#
You can manage service on remote side by using ssh (secure shell) with –H option.
[root@faraz ~]# systemctl status sshd -H [email protected] [email protected]'s password: ? sshd.service - OpenSSH server daemon Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled) Active: active (running) since Thu 2016-02-25 13:57:22 PKT; 5min ago Docs: man:sshd(8) man:sshd_config(5) Main PID: 15305 (sshd) Like init command can switch targets/runlevels similarly systemctl can switch targets/runleves mode by using command systemctl isolate runlevel(number 0 to 6).target.
[root@faraz ~]# systemctl isolate runlevel1.target [root@faraz ~]# systemctl isolate runlevel0.target or poweroff.target [root@faraz ~]# systemctl isolate runlevel1.target or rescue.target [root@faraz ~]# systemctl isolate runlevel(2,3,4).target or multi-user.target [root@faraz ~]# systemctl isolate runlevel5.target or graphical.target [root@faraz ~]# systemctl isolate runlevel6.target or reboot.target
List all the current targets by using command systemctl list-units –type=target.
[root@faraz ~]# systemctl list-units --type=target UNIT LOAD ACTIVE SUB DESCRIPTION basic.target loaded active active Basic System cryptsetup.target loaded active active Encrypted Volumes getty.target loaded active active Login Prompts graphical.target loaded active active Graphical Interface local-fs-pre.target loaded active active Local File Systems (Pre) local-fs.target loaded active active Local File Systems multi-user.target loaded active active Multi-User System network-online.target loaded active active Network is Online network.target loaded active active Network nfs-client.target loaded active active NFS client services nss-lookup.target loaded active active Host and Network Name Lookups nss-user-lookup.target loaded active active User and Group Name Lookups paths.target loaded active active Paths remote-fs-pre.target loaded active active Remote File Systems (Pre) remote-fs.target loaded active active Remote File Systems rpcbind.target loaded active active RPC Port Mapper slices.target loaded active active Slices sockets.target loaded active active Sockets swap.target loaded active active Swap sysinit.target loaded active active System Initialization timers.target loaded active active Timers
To check your default target you can use the command systemctl get-default.
You can also set the target by using command systemctl set-default graphical.target (do it yourself).
[root@faraz ~]# systemctl get-default graphical.target [root@faraz ~]#
We can also shutdown, reboot or suspend system by using systemctl command.
[root@faraz ~]# systemctl reboot [root@faraz ~]# systemctl suspend [root@faraz ~]# systemctl poweroff
To get the hostname and detail of about your Linux OS by using command hostnamectl.
[root@faraz ~]# hostnamectl Static hostname: faraz.test.server Icon name: computer-vm Chassis: vm Machine ID: 09c76cd99cd74900a5ac0a0ec93842e7 Boot ID: 6662d1aa1df0459bb0884b4db9ca1269 Virtualization: kvm Operating System: CentOS Linux 7 (Core) CPE OS Name: cpe:/o:centos:centos:7 Kernel: Linux 3.10.0-327.el7.x86_64 Architecture: x86-64 [root@faraz ~]#
In this tutorial we have discussed about linux systemd and how to use manage it using systemctl.We also practiced how to use systemctl commands to list services and to manager service by starting/stopping/enabling/disabling and checking their status. We also examined lots of other commands like journalctl, systemctl, hostnamectl with many options.
I hope you enjoyed this article with deep learning in system commands. Keep learning with us.
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