{"id":2213,"date":"2016-01-30T17:42:22","date_gmt":"2016-01-30T08:42:22","guid":{"rendered":"http:\/\/www.catracing.org\/hendrb\/?p=2213"},"modified":"2016-01-30T17:43:44","modified_gmt":"2016-01-30T08:43:44","slug":"centos-7-managing-services-using-systemctl","status":"publish","type":"post","link":"https:\/\/www.catracing.org\/hendrb\/centos-7-managing-services-using-systemctl\/","title":{"rendered":"CENTOS 7 – Managing Services Using Systemctl"},"content":{"rendered":"

\"Blog<\/span><\/h1>\n

CENTos 7 – Using Systemctl<\/span><\/h1>\n

For this months technical blog\u00a0thought I would share another difference between previous versions of the operating system.\u00a0 Which is very different and can be very confusing for those of us used to the older \u2018unix\u2019 way of doing things.\u00a0 RHEL 7, and therefor CENTos 7 have done away with the init.d method of boot scripts and starting and stopping services.\u00a0 The OS now uses systemd (Similar to Apple\u2019s launchd in OSX).\u00a0 I will not be delving into the nuts and bolts of what systemd is, and how it works.\u00a0 This is a simple run down of the commands you need to know to start, stop, and restart services using systemctl.\u00a0 Additionally I will also cover systemd\u2019s equivalent to runlevels, and how to change and set your systems default environment during boot.<\/p>\n

Starting, Stopping, and Restarting Services.<\/span><\/h2>\n

In this article I assume that you are following best practices by logging in with a standard user account and evelating your privileges using sudo. If you are not, simply ignore the sudo command.<\/p>\n

Starting a service.<\/span><\/h2>\n

Using init.d unix and Linux system, to start a service we would use the service command, which would execute it\u2019s specific startup script. Whereas in CENTos 7 you would use systemctl.<\/p>\n

Previous verions of CENTos \u2013<\/span><\/h3>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo service <service name> start<\/span><\/p>\n

CENTos 7 –<\/span><\/h3>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo systemctl start <service name><\/span><\/p>\n

Stopping a service.<\/span><\/h2>\n

<\/h3>\n

Previous versions of CENTos \u2013<\/span><\/h3>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo service <service name> stop<\/span><\/p>\n

CENTos 7 –<\/span><\/h3>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo systemctl stop <service name><\/span><\/p>\n

Restarting a service.<\/span><\/h2>\n

Previous versions of CENTos –<\/span><\/h3>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo service <service name> restart<\/span><\/p>\n

CENTos 7 –<\/span><\/h3>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo systemctl restart <service name><\/span><\/p>\n

This should all look pretty straight forward, you mostly just have to remember the new systemctl command, and the fact that you now place the action before service name.<\/p>\n

Configuring boot services,<\/span><\/h2>\n

So how do we go about configuring which services are started at boot? With init.d you could either modify your init scripts for a specific runlevel, in the rc.d directory, or use a command called chkconfig which would handle it for you.<\/p>\n

Previous versions of CENTos \u2013<\/span><\/h3>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0sudo chkconfig \u2013list sshd<\/span><\/p>\n

\u00a0\u00a0\u00a0 sshd\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0:off\u00a0\u00a0\u00a0\u00a0\u00a0 1:off\u00a0\u00a0\u00a0\u00a0\u00a0 2:on\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 3:on\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 4:on\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 5:on\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 6:off<\/em><\/span><\/p>\n

\u00a0<\/em>This\u00a0shows us that the ssd service\u00a0is either\u00a0on or\u00a0off in each corresponding runlevel. For instance runlevel 1 (Single User Mode), sshd is off at boot, however with run level (consoleonly, with networking services), sshd is on at boot.\u00a0 I do find it interesting that sshd is configured to be on in runlevel 2 (Console only, no networking.)<\/p>\n

You could easily toggle a specific service either on or off for each service with the following command.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo chkconfig <service> –level <runlevels><\/span><\/p>\n

Full example given below.<\/p>\n

\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo chkconfig sshd \u2013level 35<\/em><\/span><\/p>\n

This would in effect, toggle the sshd service to be started at boot in both run revel 3 (Multi-User, with networking, in console mode.), and runlevel 5 (Multi-User, with networking, in Graphical Environment Mode (XWindows).<\/p>\n

CENTos 7 – <\/span><\/h3>\n

In CENTos 7, You no longer have runlevels, so you only need to worry about a service being on or off (Or enabled or disabled), again using the systemctl command.<\/p>\n

To configure a service to be started at boot.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 systemctl enable <service name><\/span><\/p>\n

Full example given below. Using the secure shell daemon.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo systemctl enable sshd<\/span><\/p>\n

To no longer have a service started at boot.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 systemctl disble <service name><\/span><\/p>\n

Full example given below, Using the secure shell daemon.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo systectl disable sshd<\/span><\/p>\n

Displaying a list of running services.<\/span><\/h2>\n

You can get the status of the running services or a single service by the following 2 methods.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0systemctl status<\/span><\/p>\n

Will return the status of every running service, and its dependents.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 systemctl status <service><\/span><\/p>\n

Will display the status of an individual service (such as winbind shown here).<\/p>\n

\u251c\u2500winbind.service<\/span>
\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u2502 \u251c\u250017859 \/usr\/sbin\/winbindd<\/span>
\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u2502 \u251c\u250017998 \/usr\/sbin\/winbindd<\/span>
\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u2502 \u251c\u250019090 \/usr\/sbin\/winbindd<\/span>
\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u2502 \u251c\u250019398 \/usr\/sbin\/winbindd<\/span>
\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u2502 \u2514\u250019854 \/usr\/sbin\/winbindd<\/span><\/p>\n

The last bit I will demonstrate with system control is how to switch between a console (Command Line) environment, and how to set the default runrevel.
\nFirst let\u2019s find out what runlevel we are current using.<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo systemctl get-default<\/span><\/p>\n

The system will return the current target mode<\/span><\/p>\n

multi-user.target<\/span><\/p>\n

This is the old runrevel 3, (command line, multi user with networking).
\nSo let\u2019s say we wanted to switch to the old runlevel 5 \u201cMultiuser, Networking, with Xwindows\u201d<\/p>\n

We can have centOS return a list of available \u201cTARGETS\u201d (runlevels), You do not need to run this command as root, so no sudo is necessary.
\n
\nsystemctl list-units \u2013t target -a<\/span><\/p>\n

UNIT LOAD\u00a0\u00a0\u00a0\u00a0\u00a0 ACTIVE\u00a0\u00a0 SUB\u00a0\u00a0\u00a0 DESCRIPTION
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Basic System
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Encrypted Volumes
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 inactive dead\u00a0\u00a0 Emergency Mode
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 inactive dead\u00a0\u00a0 Final Step
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Login Prompt
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 inactive dead\u00a0\u00a0 Graphical Interface
\nlocal-fs-pre.target\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Local File Systems (Pre)
\nlocal-fs.target\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Local File Systems
\nmulti-user.target\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Multi-User System
\nnetwork-online.target\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Network is Online
\nnetwork-pre.target\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 inactive dead\u00a0\u00a0 Network (Pre)
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Network
\nnss-lookup.target\u00a0\u00a0\u00a0\u00a0\u00a0 loaded \u00a0inactive dead\u00a0\u00a0 Host and Network Name Lookups
\nnss-user-lookup.target loaded\u00a0\u00a0\u00a0 inactive dead\u00a0\u00a0 User and Group Name Lookups
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Paths
\nremote-fs-pre.target\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 inactive dead\u00a0\u00a0 Remote File Systems (Pre)
\nremote-fs.target\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Remote File System
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 inactive dead\u00a0\u00a0 Rescue Mode
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 inactive dead\u00a0\u00a0 Shutdown
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Slices
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Sockets
\ntarget\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 loaded\u00a0\u00a0\u00a0 active\u00a0\u00a0 active Sound Card<\/p>\n

For the old runlevel 5, (Xwindows, Multi-User, With Networking) we would issue the following command. As this will manipulate services, we must run this as root.
\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sudo systemctl isolate graphical.target<\/span><\/p>\n

To switch back to runlevel 3\u00a0 \u2018multi-user target’
\nsudo systemctl isolate multiuser.target<\/span><\/p>\n

Now that we can switch between targets \u201cRunlevels\u201d let\u2019s set one as a default.<\/p>\n

Remember we mentioned in the beginning of the blog that CentOS 7 now uses systemd and not init.d to control the boot process. Systemd uses a symbolic link to determine the systems default target\u201d\u00a0 If you do an ls-l or ll on \/etc\/systemd\/system, you can determine the systems default target.
\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0ll \/etc\/systemd\/system<\/span><\/p>\n