Linux Process Management and Service Commands for DevOps Engineers¶
This page explains how DevOps engineers monitor, control, and troubleshoot running processes and system services in Linux-based production environments.
systemctl Command¶
The systemctl command is used to check the status, start, stop, restart, reload, enable, and disable services.
In Linux, we have the sshd service, which is used to connect to Linux servers.
Check Service Status¶
systemctl status service_name
● sshd.service - OpenSSH server daemon
Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2023-04-20 12:34:07 GMT; 11h ago
Docs: man:sshd(8)
man:sshd_config(5)
Main PID: 26927 (sshd)
Tasks: 3
Memory: 41.3M
CGroup: /system.slice/sshd.service
├─ 2703 sshd: root [priv]
├─ 2704 sshd: root [net]
└─26927 /usr/sbin/sshd -D
Start Service¶
systemctl start service_name
httpd is the most popular web server.
[opc@new-k8s ~]$ systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: inactive (dead)
Docs: man:httpd(8)
man:apachectl(8)
[opc@new-k8s ~]$ sudo systemctl start httpd
[opc@new-k8s ~]$ sudo systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:02:49 GMT; 6s ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 22505 (httpd)
Status: "Processing requests..."
Tasks: 6
Memory: 25.6M
CGroup: /system.slice/httpd.service
├─22505 /usr/sbin/httpd -DFOREGROUND
├─22506 /usr/sbin/httpd -DFOREGROUND
├─22507 /usr/sbin/httpd -DFOREGROUND
├─22508 /usr/sbin/httpd -DFOREGROUND
├─22509 /usr/sbin/httpd -DFOREGROUND
└─22510 /usr/sbin/httpd -DFOREGROUND
Apr 21 00:02:49 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:02:49 new-k8s systemd[1]: Started The Apache HTTP Server.
Stop Service¶
systemctl stop service_name
[opc@new-k8s ~]$ sudo systemctl stop httpd
[opc@new-k8s ~]$ sudo systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: inactive (dead)
Docs: man:httpd(8)
man:apachectl(8)
Apr 21 00:02:49 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:02:49 new-k8s systemd[1]: Started The Apache HTTP Server.
Apr 21 00:04:11 new-k8s systemd[1]: Stopping The Apache HTTP Server...
Apr 21 00:04:12 new-k8s systemd[1]: Stopped The Apache HTTP Server.
Restart Service¶
systemctl restart service_name
[opc@new-k8s ~]$ sudo systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:05:06 GMT; 14s ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 23901 (httpd)
Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"
Tasks: 6
Memory: 25.6M
CGroup: /system.slice/httpd.service
├─23901 /usr/sbin/httpd -DFOREGROUND
├─23906 /usr/sbin/httpd -DFOREGROUND
├─23907 /usr/sbin/httpd -DFOREGROUND
├─23908 /usr/sbin/httpd -DFOREGROUND
├─23909 /usr/sbin/httpd -DFOREGROUND
└─23910 /usr/sbin/httpd -DFOREGROUND
Apr 21 00:05:06 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:05:06 new-k8s systemd[1]: Started The Apache HTTP Server.
[opc@new-k8s ~]$ sudo systemctl restart httpd
[opc@new-k8s ~]$ sudo systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:06:17 GMT; 16s ago
Docs: man:httpd(8)
man:apachectl(8)
Process: 24883 ExecStop=/bin/kill -WINCH ${MAINPID} (code=exited, status=0/SUCCESS)
Main PID: 24904 (httpd)
Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"
Tasks: 6
Memory: 25.1M
CGroup: /system.slice/httpd.service
├─24904 /usr/sbin/httpd -DFOREGROUND
├─24905 /usr/sbin/httpd -DFOREGROUND
├─24906 /usr/sbin/httpd -DFOREGROUND
├─24907 /usr/sbin/httpd -DFOREGROUND
├─24908 /usr/sbin/httpd -DFOREGROUND
└─24909 /usr/sbin/httpd -DFOREGROUND
Apr 21 00:06:17 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:06:17 new-k8s systemd[1]: Started The Apache HTTP Server.
Enable Service¶
If we restart our Linux system, services will be stopped and will not start automatically. To start a service automatically on boot, we need to enable it.
systemctl enable service_name
[opc@new-k8s ~]$ sudo systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:06:59 GMT; 1min 35s ago
Docs: man:httpd(8)
man:apachectl(8)
Process: 25405 ExecStop=/bin/kill -WINCH ${MAINPID} (code=exited, status=0/SUCCESS)
Main PID: 25413 (httpd)
Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"
Tasks: 6
Memory: 25.6M
CGroup: /system.slice/httpd.service
├─25413 /usr/sbin/httpd -DFOREGROUND
├─25414 /usr/sbin/httpd -DFOREGROUND
├─25415 /usr/sbin/httpd -DFOREGROUND
├─25416 /usr/sbin/httpd -DFOREGROUND
├─25417 /usr/sbin/httpd -DFOREGROUND
└─25418 /usr/sbin/httpd -DFOREGROUND
Here its mentioned the service is disabled
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
[opc@new-k8s ~]$ sudo systemctl enable httpd
Created symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.
[opc@new-k8s ~]$ sudo systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:06:59 GMT; 4min 54s ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 25413 (httpd)
Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"
CGroup: /system.slice/httpd.service
├─25413 /usr/sbin/httpd -DFOREGROUND
├─25414 /usr/sbin/httpd -DFOREGROUND
├─25415 /usr/sbin/httpd -DFOREGROUND
├─25416 /usr/sbin/httpd -DFOREGROUND
├─25417 /usr/sbin/httpd -DFOREGROUND
└─25418 /usr/sbin/httpd -DFOREGROUND
Apr 21 00:06:59 new-k8s systemd[1]: Stopped The Apache HTTP Server.
Apr 21 00:06:59 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:06:59 new-k8s systemd[1]: Started The Apache HTTP Server.
Now the service is enabled
Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
Disable Service¶
systemctl disable service_name
[opc@new-k8s ~]$ sudo systemctl disable httpd
Removed symlink /etc/systemd/system/multi-user.target.wants/httpd.service.
[opc@new-k8s ~]$ sudo systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:06:59 GMT; 8min ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 25413 (httpd)
Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"
CGroup: /system.slice/httpd.service
├─25413 /usr/sbin/httpd -DFOREGROUND
├─25414 /usr/sbin/httpd -DFOREGROUND
├─25415 /usr/sbin/httpd -DFOREGROUND
├─25416 /usr/sbin/httpd -DFOREGROUND
├─25417 /usr/sbin/httpd -DFOREGROUND
└─25418 /usr/sbin/httpd -DFOREGROUND
Apr 21 00:06:59 new-k8s systemd[1]: Stopped The Apache HTTP Server.
Apr 21 00:06:59 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:06:59 new-k8s systemd[1]: Started The Apache HTTP Server.
Now the service is disabled
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
service Command¶
service is a "high-level" command used for starting and stopping services in different Unix/Linux systems. Depending on the "lower-level" service manager, service redirects to different binaries.
For example, on CentOS 7 it redirects to systemctl, while on CentOS 6 it directly calls the relative /etc/init.d script. On the other hand, in older Ubuntu releases it redirects to upstart.
service is adequate for basic service management, while directly calling systemctl gives greater control options.
Check Status (service)¶
service service_name status
[opc@new-k8s ~]$ sudo service httpd status
Redirecting to /bin/systemctl status httpd.service
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:06:59 GMT; 11min ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 25413 (httpd)
Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"
CGroup: /system.slice/httpd.service
├─25413 /usr/sbin/httpd -DFOREGROUND
├─25414 /usr/sbin/httpd -DFOREGROUND
├─25415 /usr/sbin/httpd -DFOREGROUND
├─25416 /usr/sbin/httpd -DFOREGROUND
├─25417 /usr/sbin/httpd -DFOREGROUND
└─25418 /usr/sbin/httpd -DFOREGROUND
Apr 21 00:06:59 new-k8s systemd[1]: Stopped The Apache HTTP Server.
Apr 21 00:06:59 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:06:59 new-k8s systemd[1]: Started The Apache HTTP Server.
Stop Service (service)¶
service service_name stop
[opc@new-k8s ~]$ sudo service httpd stop
Redirecting to /bin/systemctl stop httpd.service
[opc@new-k8s ~]$ sudo service httpd status
Redirecting to /bin/systemctl status httpd.service
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: inactive (dead)
Docs: man:httpd(8)
man:apachectl(8)
Start Service (service)¶
service service_name start
[opc@new-k8s ~]$ sudo service httpd start
Redirecting to /bin/systemctl start httpd.service
[opc@new-k8s ~]$ sudo service httpd status
Redirecting to /bin/systemctl status httpd.service
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:20:25 GMT; 3s ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 2170 (httpd)
Status: "Processing requests..."
Tasks: 6
Memory: 25.5M
CGroup: /system.slice/httpd.service
├─2170 /usr/sbin/httpd -DFOREGROUND
├─2171 /usr/sbin/httpd -DFOREGROUND
├─2172 /usr/sbin/httpd -DFOREGROUND
├─2173 /usr/sbin/httpd -DFOREGROUND
├─2174 /usr/sbin/httpd -DFOREGROUND
└─2175 /usr/sbin/httpd -DFOREGROUND
Restart Service (service)¶
service service_name restart
[opc@new-k8s ~]$ sudo service httpd restart
Redirecting to /bin/systemctl restart httpd.service
[opc@new-k8s ~]$ sudo service httpd status
Redirecting to /bin/systemctl status httpd.service
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Fri 2023-04-21 00:21:58 GMT; 7s ago
Docs: man:httpd(8)
man:apachectl(8)
Process: 3419 ExecStop=/bin/kill -WINCH ${MAINPID} (code=exited, status=0/SUCCESS)
Main PID: 3433 (httpd)
Status: "Processing requests..."
Tasks: 6
Memory: 25.5M
CGroup: /system.slice/httpd.service
├─3433 /usr/sbin/httpd -DFOREGROUND
├─3434 /usr/sbin/httpd -DFOREGROUND
├─3435 /usr/sbin/httpd -DFOREGROUND
├─3436 /usr/sbin/httpd -DFOREGROUND
├─3437 /usr/sbin/httpd -DFOREGROUND
└─3438 /usr/sbin/httpd -DFOREGROUND
NOTE: We cannot use the service command to enable and disable services.
ps Command¶
The ps command is used to list all running background processes.
ps -ef | grep -i sshd
Lets see only sshd process
[opc@new-k8s ~]$ ps -ef | grep -i sshd
opc 6009 32710 0 00:26 pts/0 00:00:00 grep --color=auto -i sshd
root 26927 1 0 Apr20 ? 00:00:02 /usr/sbin/sshd -D
root 32685 26927 0 Apr20 ? 00:00:00 sshd: opc [priv]
root 32700 26927 0 Apr20 ? 00:00:00 sshd: opc [priv]
opc 32709 32685 0 Apr20 ? 00:00:00 sshd: opc@pts/0
opc 32755 32700 0 Apr20 ? 00:00:00 sshd: opc@notty
This is the running process info for sshd, it has process id 26927
root 26927 1 0 Apr20 ? 00:00:02 /usr/sbin/sshd -D
🧠 Quick Quiz — Process & Service Management¶
#
Which command is used to manage services on modern Linux systems?
📝 Want More Practice?¶
To strengthen your understanding and prepare for interviews, try the full 20-question practice quiz based on this chapter:
👉 Start Process & Service Management Quiz (20 Questions)
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