kill Cheatsheet
Quick reference for sending signals to processes by PID with kill and killall in Linux
The `kill` command sends signals to processes by PID. Use it to stop, reload, or pause a process. This cheatsheet covers common signals, kill by PID, `killall` by name, background job control, and a full signal reference.
Basic Syntax
Core kill command forms.
| Command | Description |
|---|---|
kill PID | Send SIGTERM (graceful stop) to a process |
kill -9 PID | Force kill a process (SIGKILL) |
kill -1 PID | Reload process config (SIGHUP) |
kill -l | List all available signal names and numbers |
kill -0 PID | Check if a PID exists without sending a signal |
Signal Reference
Signals most commonly used with kill, killall, and pkill.
| Signal | Number | Description |
|---|---|---|
SIGHUP | 1 | Reload config — most daemons reload settings without restarting |
SIGINT | 2 | Interrupt process — equivalent to pressing Ctrl+C |
SIGQUIT | 3 | Quit and write a core dump for debugging |
SIGKILL | 9 | Force kill — cannot be caught or ignored; always terminates immediately |
SIGTERM | 15 | Graceful stop — default signal; process can clean up before exiting |
SIGUSR1 | 10 | User-defined signal 1 — meaning depends on the application |
SIGUSR2 | 12 | User-defined signal 2 — meaning depends on the application |
SIGCONT | 18 | Resume a process that was suspended with SIGSTOP |
SIGSTOP | 19 | Suspend process — cannot be caught or ignored |
SIGTSTP | 20 | Terminal stop — equivalent to pressing Ctrl+Z |
Kill by PID
Send signals to one or more specific processes.
| Command | Description |
|---|---|
kill 1234 | Gracefully stop PID 1234 |
kill -9 1234 5678 | Force kill multiple PIDs at once |
kill -HUP 1234 | Reload config for PID 1234 |
kill -STOP 1234 | Suspend PID 1234 |
kill -CONT 1234 | Resume suspended PID 1234 |
kill -9 $(pidof firefox) | Force kill all PIDs for a process by name |
killall: Kill by Name
Send signals to all processes matching an exact name.
| Command | Description |
|---|---|
killall process_name | Send SIGTERM to all matching processes |
killall -9 process_name | Force kill all matching processes |
killall -HUP nginx | Reload all nginx processes |
killall -u username process_name | Kill matching processes owned by a user |
killall -v process_name | Kill and report which processes were signaled |
killall -r "pattern" | Match process names with a regex pattern |
Background Jobs
Kill jobs running in the current shell session.
| Command | Description |
|---|---|
jobs | List background jobs and their job numbers |
kill %1 | Send SIGTERM to background job number 1 |
kill -9 %1 | Force kill background job number 1 |
kill %+ | Kill the most recently started background job |
kill %% | Kill the current (most recent) background job |
Troubleshooting
Quick fixes for common kill issues.
| Issue | Check |
|---|---|
Process does not stop after SIGTERM | Wait a moment, then escalate to kill -9 PID |
No such process error | PID has already exited; verify with ps -p PID |
Operation not permitted | Process belongs to another user — use sudo kill PID |
SIGKILL has no effect | Process is in uninterruptible sleep (D state in ps); only a reboot can free it |
| Not sure which PID to kill | Find it first with pidof name, pgrep name, or ps aux | grep name |
Related Guides
| Guide | Description |
|---|---|
| kill Command in Linux | Full guide to kill options, signals, and examples |
| How to Kill a Process in Linux | Practical walkthrough for finding and stopping processes |
| pkill Command in Linux | Kill processes by name and pattern |
| pgrep Command in Linux | Find process PIDs before signaling |
| ps Command in Linux | Inspect the running process list |
