Today I was trying to learn and know about Systemd. I have found one of the great Article, Sharing with you guys, It will help you to understand this biggest and major change in RHEL and CentOS 7.
This article is not mine, I found on internet and felt that this is wonderful Article so Sharing with you all, Thanks to Original author, Given credit to him at the end of article.
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 (Systemd calls them units).
The Systemd configuration is stored in the /etc/systemd directory.
Systemd primary task is to manage the boot process and provides informations about it.
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
Note: You will find additional information on this point in the Lennart Poettering’s blog.
In addition, Systemd handles the system event log, a syslog daemon is not mandatory any more.
To get the content of the Systemd journal, type:
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
Systemd organizes tasks in control groups. For example, all the processes started by an apache webserver 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.
To get the current CPUShares service value, type:
# systemctl show -p CPUShares httpd.service
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 the systemctl 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.
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
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 NTP service, type:
# systemctl status ntpd ntpd.service Loaded: not-found (Reason: No such file or directory) Active: inactive (dead)
If you change a service configuration, you will need to reload it:
# systemctl daemon-reload
To get the list of all the units (services, mount points, devices) with their status and description, type:
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 process (here httpd) on a remote server (here rhel7.example.com), type:
# systemctl -H firstname.lastname@example.org status httpd.service
Systemd also deals with run levels. As everything is represented by files in Systemd, target files replace run levels.
To move to single user mode, type:
# systemctl rescue
To move to the level 3 (equivalent to the previous level 3), type:
# systemctl isolate runlevel3.target
# 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
Systemd‘s authors have decided to help Linux standardization among distributions. Through Systemd, changes happen in the localization of some configuration files.
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.
To assign the rhel7 hostname permanently to the server, type:
# hostnamectl set-hostname rhel7
Note: With this syntax all 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
For a better understanding, you can additionally read Bob Cromwell’s blog about Systemd.
Thanks to Original Author for explaining it very nicely.
Enjoy Systemd Enjoy RHEL 7 Enjoy CentOS 7 Enjoy
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