{"id":730,"date":"2016-12-07T10:43:15","date_gmt":"2016-12-07T19:43:15","guid":{"rendered":"\/blog\/?p=730"},"modified":"2023-09-21T09:37:50","modified_gmt":"2023-09-21T00:37:50","slug":"systemd","status":"publish","type":"post","link":"https:\/\/hasu0707.duckdns.org\/blog\/?p=730","title":{"rendered":"systemd"},"content":{"rendered":"\n

systemd documentation<\/span><\/h2>

systemd has very comprehensive documentation. Refer to<\/span><\/p>\r\n\r\n<\/span>

http:\/\/0pointer.de\/blog\/projects\/systemd-docs.html<\/span><\/a><\/p>\r\n\r\n<\/span>

Boot Kernel Command Line<\/span><\/h2>

On boot <\/span>systemd<\/span><\/strong> activates (by default), the target unit <\/span>default.target<\/span><\/em> whose job is to activate services and other units by pulling them in via dependencies.<\/span><\/p>\r\n\r\n<\/span>

To override the unit to activate, <\/span>systemd<\/span><\/strong> parses its own kernel command line arguments via the <\/span>systemd.unit=<\/span><\/code> command line option. This may be used to temporarily boot into a different boot unit. The classical run-levels are replaced as following:<\/span><\/p>\r\n\r\n<\/span>

systemd.unit=rescue.target<\/span><\/code> is a special target unit for setting up the base system and a rescue shell (similar to run level 1); <\/span>systemd.unit=emergency.target<\/span><\/code>, is very similar to passing <\/span>init=\/bin\/sh<\/span><\/code> but with the option to boot the full system from there; <\/span>systemd.unit=multi-user.target<\/span><\/code> for setting up a non-graphical multi-user system; <\/span>systemd.unit=graphical.target<\/span><\/code> for setting up a graphical login screen.<\/span><\/p>\r\n\r\n<\/span>

For details about these special systemd boot units, view the man <\/span>systemd.special<\/span><\/code> page. it scripts<\/span><\/p>\r\n\r\n<\/span>

What is the tool to manage services with systemd?<\/span><\/h2>

systemctl is the primary tool to use. It combines the functionality of both service and chkconfig into a single tool that you can use for instance to enable\/disable services permanently or only for the current session.<\/span><\/p>\r\n\r\n<\/span>

list all running services etc:<\/span><\/p>\r\n\r\n<\/span>

 systemctl <\/span><\/pre>
Refer to man systemctl for more details. systemd-cgls lists the running process in a tree format. It can recursively show the content of any given control group. Refer to man systemd-cgls for more details.<\/span><\/p>\r\n\r\n<\/span>
How do I start\/stop or enable\/disable services?<\/span><\/h2>
Activates a service immediately:<\/span><\/p>\r\n\r\n<\/span>
  systemctl start foo <\/span><\/pre>
Deactivates a service immediately:<\/span><\/p>\r\n\r\n<\/span>
  systemctl stop foo <\/span><\/pre>
Restarts a service:<\/span><\/p>\r\n\r\n<\/span>
 systemctl restart foo <\/span><\/pre>
Shows status of a service including whether it is running or not:<\/span><\/p>\r\n\r\n<\/span>
 systemctl status foo <\/span><\/pre>
Enables a service to be started on bootup:<\/span><\/p>\r\n\r\n<\/span>
 systemctl enable foo <\/span><\/pre>
Disables a service to not start during bootup:<\/span><\/p>\r\n\r\n<\/span>
 systemctl disable foo <\/span><\/pre>
Prevent a service from starting dynamically or even manually unless unmasked:<\/span><\/p>\r\n\r\n<\/span>
 systemctl mask foo <\/span><\/pre>
Check whether a service is already enabled or not:<\/span><\/p>\r\n\r\n<\/span>
 systemctl is-enabled foo<\/span><\/pre>
Refer to man systemctl for more details.<\/span><\/p>\r\n\r\n<\/span>
How do I change the target (runlevel)?<\/span><\/h2>
systemd has the concept of targets which is a more flexible replacement for runlevels in sysvinit.<\/span><\/p>\r\n\r\n<\/span>
Run level 3 is emulated by multi-user.target. Run level 5 is emulated by graphical.target. runlevel3.target is a symbolic link to multi-user.target and runlevel5.target is a symbolic link to graphical.target.<\/span><\/p>\r\n\r\n<\/span>
You can switch to 'runlevel 3' by running<\/span><\/p>\r\n\r\n<\/span>
 systemctl isolate multi-user.target <\/span><\/pre>
You can switch to 'runlevel 5' by running<\/span><\/p>\r\n\r\n<\/span>
 systemctl isolate graphical.target <\/span><\/pre>
How do I change the default target?<\/span><\/h2>
 systemctl set-default <name of target>.target <\/span><\/pre>
graphical.target is the default. You might want multi-user.target for the equivalent of non graphical (runlevel 3) from sysv init. The full list of targets can be accessed via systemctl list-units --type=target<\/span><\/p>\r\n\r\n<\/span>
systemd does not use \/etc\/inittab file.<\/span><\/p>\r\n\r\n<\/span>
How do I know the current target?<\/span><\/h2>
 systemctl get-default <\/span><\/pre>
How to power off the machine?<\/span><\/h2>
You can use<\/span><\/p>\r\n\r\n<\/span>
 poweroff <\/span><\/pre>
Some more possibilities are: <\/span>halt -p<\/span><\/code>, <\/span>init 0<\/span><\/code>, <\/span>shutdown -P now<\/span><\/code><\/p>\r\n\r\n<\/span>
Note that <\/span>halt<\/span><\/code> used to work the same as <\/span>poweroff<\/span><\/code> in previous Fedora releases, but systemd distinguishes between the two, so <\/span>halt<\/span><\/code>without parameters now does exactly what it says - it merely stops the system without turning it off.<\/span><\/p>\r\n\r\n<\/span>
Does service command work with systemd?<\/span><\/h2>
Yes. It has been modified to call systemctl automatically when dealing with systemd service files. So either of the following commands does the same thing<\/span><\/p>\r\n\r\n<\/span>

<\/p>\r\n\r\n<\/span>
 systemctl stop NetworkManager <\/span><\/pre>
(or)<\/span><\/p>\r\n\r\n<\/span>
 service NetworkManager stop <\/span><\/pre>
Does chkconfig command work with systemd?<\/span><\/h2>
Yes, for turning on\/off services, compatibility has been provided both ways. chkconfig has been modified to call systemctl when dealing with systemd service files. Also systemctl automatically calls chkconfig when dealing with a traditional sysv init file.<\/span><\/p>\r\n\r\n<\/span>
So either of the following commands does the same thing<\/span><\/p>\r\n\r\n<\/span>
 systemctl disable NetworkManager <\/span><\/pre>
(or)<\/span><\/p>\r\n\r\n<\/span>
 chkconfig NetworkManager off <\/span><\/pre>
chkconfig --list doesn't list systemd services, only Sys V services. The output of chkconfig takes note of this, along with supplying additional information.<\/span><\/p>\r\n\r\n<\/span>
Does system-config-services work with systemd?<\/span><\/h2>
Yes. It does.<\/span><\/p>\r\n\r\n<\/span>
How do I change the number of gettys running by default?<\/span><\/h2>
The simplest way is to edit \/etc\/systemd\/logind.conf (<\/span>man page<\/span><\/a>):<\/span><\/p>\r\n\r\n<\/span>
[Login]\r\n...\r\nNAutoVTs=8\r\n<\/span><\/pre>
This setting will take effect after reboot.<\/span><\/p>\r\n\r\n<\/span>
Alternatively, getty@.services which open the login prompt can be enabled and started individually.<\/span><\/p>\r\n\r\n<\/span>
To add another getty:<\/span><\/p>\r\n\r\n<\/span>
systemctl enable getty@tty8\r\nsystemctl start getty@tty8\r\n<\/span><\/pre>
To remove a getty:<\/span><\/p>\r\n\r\n<\/span>
systemctl disable getty@tty8\r\nsystemctl stop getty@tty8\r\n<\/span><\/pre>
systemd does not use \/etc\/inittab file.<\/span><\/p>\r\n\r\n<\/span>
How do I set automatic login on a virtual console terminal?<\/span><\/h2>
First create a new service similar to getty@.service:<\/span><\/p>\r\n\r\n<\/span>
# cp \/lib\/systemd\/system\/getty@.service \\\r\n     \/etc\/systemd\/system\/autologin@.service\r\n# ln -s \/etc\/systemd\/system\/autologin@.service \\\r\n        \/etc\/systemd\/system\/getty.target.wants\/getty@tty8.service\r\n<\/span><\/pre>
then edit ExecStart, Restart and Alias values, like this:<\/span><\/p>\r\n\r\n<\/span>
...\r\nExecStart=-\/sbin\/mingetty --autologin USERNAME %I\r\nRestart=no\r\n...\r\nAlias=getty.target.wants\/getty@tty8.service\r\n<\/span><\/pre>
and finally reload daemon and start the service:<\/span><\/p>\r\n\r\n<\/span>
systemctl daemon-reload\r\nsystemctl start getty@tty8.service\r\n<\/span><\/pre>
Note that if you exit tty8 session, you wont be able to use it until next reboot or manual start by systemctl, except if you leave Restart as 'always', but I highly recommend to avoid this according to security reasons.<\/span><\/p>\r\n\r\n<\/span>
How do I customize a unit file\/ add a custom unit file?<\/span><\/h2>
The best way to customize unit files is to add \/etc\/systemd\/system\/foobar.service.d\/*.conf where foobar.service is the name of the service you want to customize. If a directory doesn't already exist, create one and drop a conf file with the settings you want to override. For example,<\/span><\/p>\r\n\r\n<\/span>
\/etc\/systemd\/system\/httpd.service.d\/restart.conf<\/span><\/p>\r\n\r\n<\/span>
[Service]\r\nRestart=always\r\nRestartSec=30\r\n<\/span><\/pre>
Refer to man <\/span>systemd.unit<\/span><\/a> page for more details.<\/span><\/p>\r\n\r\n<\/span>
\"Idea.png\"<\/a><\/div>
Don't forget to reload systemd daemon using <\/span>systemctl daemon-reload<\/span><\/code> and <\/span>systemctl restart foobar<\/span><\/code> after editing a unit file where foobar is the name of the unit. Also note that you can <\/span>systemd-delta <\/span><\/code>to list the unit files which have been customized and also the precise differences <\/span><\/strong>
<\/div><\/div>
Special care must be taken when overriding options which can be set muliple times (<\/span>ExecStart<\/span><\/code>, <\/span>ExecStartPre<\/span><\/code>, <\/span>ExecStartPost<\/span><\/code> are a common example). Assigning some value to the option <\/span>appends<\/span><\/em> to the existing list, while assiging the <\/span>empty<\/span><\/em> value <\/span>resets<\/span><\/em> the list.<\/span><\/p>\r\n\r\n<\/span>
For example, let's say we have a service file like this:<\/span><\/p>\r\n\r\n<\/span>
[Service]\r\nExecStart=\/bin\/echo execstart1\r\nExecStart=\r\nExecStart=\/bin\/echo execstart2\r\nExecStartPost=\/bin\/echo post1\r\nExecStartPost=\/bin\/echo post2\r\n<\/span><\/pre>
When started, this service will print<\/span><\/p>\r\n\r\n<\/span>
execstart2\r\npost1\r\npost2\r\n<\/span><\/pre>
The same rules apply to snippets in <\/span>.d<\/span><\/code> directories. This means that snippets which override <\/span>ExecStart<\/span><\/code> and similar settings, often should start with the empty assignment <\/span>ExecStart=<\/span><\/code>, followed by the new setting.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"
systemd documentation systemd has very comprehensive documentation. Refer to http:\/\/0pointer.de\/blog\/projects\/systemd-docs.html Boot Kernel Command Line On boot systemd activates (by default), the target unit default.target whose job is to activate services and other units by pulling them in via dependencies. To override the unit to activate, systemd parses its own kernel command line arguments via the systemd.unit= command line option. This may be used […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_import_markdown_pro_load_document_selector":0,"_import_markdown_pro_submit_text_textarea":"","site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[39],"tags":[],"class_list":["post-730","post","type-post","status-publish","format-standard","hentry","category-os_linux_unix_macos"],"_links":{"self":[{"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=\/wp\/v2\/posts\/730","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=730"}],"version-history":[{"count":0,"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=\/wp\/v2\/posts\/730\/revisions"}],"wp:attachment":[{"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=730"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=730"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/hasu0707.duckdns.org\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=730"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}