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.
find Command¶
The find command is used to search for files or directories.
[opc@new-k8s ~]$ ll
total 3072036
-rw-rw-r--. 1 opc opc 852 Apr 15 03:15 fruits.txt
-rw-rw-r--. 1 opc opc 43 Apr 19 12:38 hello.txt
-rw-rw-r--. 1 opc opc 9943 Apr 19 11:16 india.txt
-rwxrwxr-x. 1 opc opc 81 Apr 15 13:27 newtest
-rw-rw-r--. 1 opc opc 2026 Apr 19 12:06 output.json
drwxrwxr-x. 2 opc opc 25 Nov 26 2021 prometheus
-rw-rw-r--. 1 opc opc 282 Apr 19 12:34 states.txt
-rw-r--r--. 1 root root 3145728000 Jan 11 2022 swapfile
drwxrwxr-x. 4 opc opc 100 Apr 15 13:04 test
-rw-rw-r--. 1 opc opc 74 Apr 19 12:11 test.json
[opc@new-k8s ~]$ pwd
/home/opc
[opc@new-k8s ~]$ find ./ -name test.json
./test.json
You can also find files in a different folder.
[opc@new-k8s ~]$ pwd
/home/opc
[opc@new-k8s ~]$ ll /tmp
total 8
-rw-------. 1 root root 1097 Apr 20 08:40 dhclient-exit-hooksPuY.log
-rw-rw-r--. 1 opc opc 2026 Apr 20 11:14 output.json
[opc@new-k8s ~]$ find /tmp -name output.json
/tmp/output.json
You can also find the file in whole file system, but it will take some time, it will check all files and directories
find: ‘/var/spool/at’: Permission denied
find: ‘/root’: Permission denied
/tmp/output.json
find: ‘/usr/share/polkit-1/rules.d’: Permission denied
find: ‘/usr/libexec/initscripts/legacy-actions/auditd’: Permission denied
/home/opc/output.json
find: ‘/home/vignesh’: Permission denied
find: ‘/opt/containerd’: Permission denied
Find Empty Files & Directories¶
[opc@new-k8s ~]$ find ./ -empty
./test/server
./test/client/server-client
./test/hello.txt
./test/vignesh/mani/raghav
Find Empty Files Only¶
[opc@new-k8s ~]$ find ./ -type f -empty
./test/server
./test/client/server-client
./test/hello.txt
Find Empty Directories Only¶
[opc@new-k8s ~]$ find ./ -type d -empty
./test/vignesh/mani/raghav
Find and Delete Empty Files¶
find ./ -type f -empty -exec rm -i {} ;
locate Command¶
The locate command is used for quickly finding files and directories.
The locate command doesn't search the entire filesystem, but looks through a regularly updated file database in the system. Thus, the search completes much faster.
-i → ignore case
[opc@new-k8s ~]$ locate hello
/home/opc/hello.txt
/home/opc/test/hello.txt
Sometimes, even deleted files are shown in the output of the locate command because it's not updated yet in the locate database.
-e → argument to search the filesystem (checks existence)
[opc@new-k8s ~]$ pwd
/home/opc
[opc@new-k8s ~]$ ll
total 3072032
-rw-rw-r--. 1 opc opc 852 Apr 15 03:15 fruits.txt
-rw-rw-r--. 1 opc opc 0 Apr 20 11:46 hello.txt
-rw-rw-r--. 1 opc opc 9943 Apr 19 11:16 india.txt
-rwxrwxr-x. 1 opc opc 81 Apr 15 13:27 newtest
-rw-rw-r--. 1 opc opc 2026 Apr 19 12:06 output.json
drwxrwxr-x. 2 opc opc 25 Nov 26 2021 prometheus
-rw-rw-r--. 1 opc opc 282 Apr 19 12:34 states.txt
-rw-r--r--. 1 root root 3145728000 Jan 11 2022 swapfile
drwxrwxr-x. 4 opc opc 86 Apr 20 11:46 test
-rw-rw-r--. 1 opc opc 74 Apr 19 12:11 test.json
[opc@new-k8s ~]$ locate hello.txt
/home/opc/hello.txt
/home/opc/test/hello.txt
[opc@new-k8s ~]$ rm -f hello.txt
[opc@new-k8s ~]$ locate hello.txt
/home/opc/hello.txt
/home/opc/test/hello.txt
[opc@new-k8s ~]$ locate -e hello.txt
/home/opc/test/hello.txt
sort Command¶
[opc@new-k8s ~]$ cat states.txt
Andhra Pradesh
Arunachal Pradesh
Assam
Bihar
Chhattisgarh
Gujarat
Haryana
Tamil Nadu
Himachal Pradesh
Jharkhand
Karnataka
Kerala
Maharashtra
Madhya Pradesh
Manipur
Meghalaya
Mizoram
Nagaland
Odisha
Punjab
Rajasthan
Sikkim
Tripura
Telangana
Uttar Pradesh
Uttarakhand
West Bengal
Goa
[opc@new-k8s ~]$ cat states.txt | sort
Andhra Pradesh
Arunachal Pradesh
Assam
Bihar
Chhattisgarh
Goa
Gujarat
Haryana
Himachal Pradesh
Jharkhand
Karnataka
Kerala
Madhya Pradesh
Maharashtra
Manipur
Meghalaya
Mizoram
Nagaland
Odisha
Punjab
Rajasthan
Sikkim
Tamil Nadu
Telangana
Tripura
Uttarakhand
Uttar Pradesh
West Bengal
uniq Command¶
[opc@new-k8s ~]$ cat names.txt
I love devops.
I love devops.
I love devops.
I love music.
I love movies.
I love movies.
[opc@new-k8s ~]$ cat names.txt | uniq
I love devops.
I love music.
I love movies.
[opc@new-k8s ~]$ cat names.txt | uniq -c
3 I love devops.
1
1 I love music.
2 I love movies.
Lines which are repeated only
[opc@new-k8s ~]$ uniq -d names.txt
I love devops.
I love movies.
Lines which are uniq
[opc@new-k8s ~]$ uniq -u names.txt
I love music.
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 ${MAINPID} (code=exited, status=0/SUCCESS)
Main PID: 3433 (httpd)
Status: "Processing requests..."
Tasks: 6
Memory: 25.5M
CGroup: /system.slice/httpd.service
├─3433 /usr/sbin/httpd -DFOREGROUND
├─3434 /usr/sbin/httpd -DFOREGROUND
├─3435 /usr/sbin/httpd -DFOREGROUND
├─3436 /usr/sbin/httpd -DFOREGROUND
├─3437 /usr/sbin/httpd -DFOREGROUND
└─3438 /usr/sbin/httpd -DFOREGROUND
NOTE: We cannot use the service command to enable and disable services.
journalctl Command¶
The journalctl command is used to check the logs of a service.
journalctl -u service_name
[opc@new-k8s ~]$ journalctl -u httpd
-- Logs begin at Tue 2023-04-18 15:19:48 GMT, end at Fri 2023-04-21 00:24:03 GMT. --
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.
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.
Apr 21 00:06:16 new-k8s systemd[1]: Stopping The Apache HTTP Server...
Apr 21 00:06:17 new-k8s systemd[1]: Stopped The Apache HTTP Server.
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.
Apr 21 00:06:58 new-k8s systemd[1]: Stopping The Apache HTTP Server...
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.
Apr 21 00:19:45 new-k8s systemd[1]: Stopping The Apache HTTP Server...
Apr 21 00:19:46 new-k8s systemd[1]: Stopped The Apache HTTP Server.
Apr 21 00:20:25 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:20:25 new-k8s systemd[1]: Started The Apache HTTP Server.
Apr 21 00:21:57 new-k8s systemd[1]: Stopping The Apache HTTP Server...
Apr 21 00:21:58 new-k8s systemd[1]: Stopped The Apache HTTP Server.
Apr 21 00:21:58 new-k8s systemd[1]: Starting The Apache HTTP Server...
Apr 21 00:21:58 new-k8s systemd[1]: Started The Apache HTTP Server.
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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