pkill Command in Linux
The pkill command in Linux sends signal processes based on their names or attributes such as user, group, or terminal. By default, it sends a SIGTERM signal to processes to terminate them. It can be case-sensitive and supports regular expressions (regex) for pattern matching. It is part of the procps (procps-ng) package.
Table of Contents
Here is a comprehensive guide to the options available with the pkill command −
Syntax of pkill Command
The syntax of the Linux pkill command is as follows −
pkill [options] [pattern]
In the above syntax, the [options] field is used to specify various options to modify how the matching is performed or specify which processes to target. The [pattern] field is used to specify the name or regular expression to match against the process name.
pkill Command Options
The options of the pkill command are listed below −
| Flags | Options | Description |
|---|---|---|
| --signal signal | Defines the signal to send to each matched process. Either numeric or symbolic signal names can be used | |
| -c | --count | Suppress normal output; instead, print a count of matching processes |
| -d delimiter | --delimiter delimiter | Sets the string used to delimit each process ID in the output (default: newline) |
| -e | --echo | Display the name and PID of the process being killed |
| -f | --full | Match against the full command line instead of just the process name |
| -g pgrp,... | --pgroup pgrp,... | Match processes in the listed process group IDs |
| -G gid,... | --group gid,... | Match processes by their real group ID, using numeric or symbolic values |
| -i | --ignore-case | Perform case-insensitive matching |
| -l | --list-name | List the process name and process ID |
| -n | --newest | Select only the newest of the matching processes |
| -o | --oldest | Select only the oldest of the matching processes |
| -O secs | --older secs | Select processes older than the specified seconds |
| -P ppid,... | --parent ppid,... | Match processes by their parent process ID |
| -s sid,... | --session sid,... | Match processes by their session ID |
| -t term,... | --terminal term,... | Match processes by their controlling terminal |
| -u euid,... | --euid euid,... | Match processes by effective user ID |
| -U uid,... | --uid uid,... | Match processes by real user ID |
| -v | --inverse | Negate the matching |
| -w | --lightweight | Show all thread IDs instead of process IDs |
| -x | --exact | Match processes exactly by name or command line |
| -F file | --pidfile file | Read PIDs from a specified file |
| -L | --logpidfile | Fail if the specified pidfile is not locked |
| -r D,R,S,Z,... | --runstates D,R,S,Z,... | Match processes by their state |
| -A | --ignore-ancestors | Ignore all ancestors of the command |
| -H | --require-handler | Match processes with a userspace signal handler for the signal |
| --cgroup name,... | Match processes by control group (cgroup) v2 name | |
| --ns pid | Match processes in the same namespaces. Requires root | |
| --nslist name,... | Match only the provided namespaces (e.g., ipc, mnt, net) | |
| -q value | --queue value | Use sigqueue with an integer value for the signal |
| -V | --version | Display version information and exit |
| -h | --help | Display help and exit |
Examples of pkill Command in Linux
This section demonstrates the usage of the pkill command in Linux with examples.
Killing a Process by Name
To kill a process by name, use the pkill command with the process name. For example, to kill the vim process, use the following command −
pkill vim
Killing a Process by Name with Case-Insensitivity Enabled
To kill a process by name with case-insensitivity, use the -i or --ignore-case option −
pkill -i Vim
Killing the Most Recent Process
To kill the most recently started process from the matching processes, use the -n or --newest option −
pkill -n firefox
The above command kills the newest firefox process based on its start time. If multiple firefox instances are running, it targets the one that was started most recently.
Killing the Oldest Process
To kill the oldest process among the matching process, use the -o or --oldest option with the process name −
pkill -o firefox
Sending a Specific Signal
To send a specific signal, specify the signal name with the process. For example, to send an HUP signal, use the following command −
pkill -HUP vim
Other signals that can be used with the pkill command are listed below −
| Signal | Number | Description |
|---|---|---|
| TERM | 15 | Gracefully terminate a process (default). |
| KILL | 9 | Forcefully terminate a process. |
| STOP | 19 | Pause a process. |
| CONT | 18 | Resume a paused process. |
Note that not all processes are responsive to STOP and CONT signals.
Killing All Processes by a Group ID
Use the -G or --group option to kill all the processes by a group ID. For example, to kill processes associated with GID 994, use the following command −
pkill -G 994
To list the groups with their IDs, use the following command −
getent group
Killing All Processes of a Specific User ID
To kill all processes of a specific user, use the -U or --UID with the user ID −
pkill -U 1001
To list UIDs, use the following command −
getent passwd
To get the user ID of a specific user, use the id command with the userâs name −
id -u alex
Killing a Process by Parent Process ID
To kill a process by its parent PID, use the -P or --parent option −
pkill -P 4567
To get the parent process of a process, use the following command −
ps -o ppid= -p 4772
Displaying a Killed Process Name and ID
To display the killed process name and ID, use the -e or --echo option with the pkill command −
pkill -e vim
Killing Processes on a Specific Terminal
To kill processes associated with a specific terminal, use the -t or --terminal option with the terminal name.
pkill -t tty1
Displaying Usage Help
To display the usage help of the pkill command, use the -h or --help option:
pkill --help
Conclusion
The pkill command in Linux is a powerful tool for terminating processes based on various criteria such as process name, user, group, or terminal. It allows specifying different signals, matching processes using regular expressions, and filtering processes with several options like case-insensitive matching, listing processes, and targeting processes by specific attributes such as parent PID or group ID.
The pkill command provides an efficient way to manage processes without needing to identify each one manually. It is part of the procps package and is widely used for process management tasks.