# pkill
Signal processes based on name and other attributes.
## Description
Looks up processes based on name and other attributes, then sends a signal to
each matching process. Uses the same matching logic as pgrep. By default, sends
SIGTERM.
## Inputs
- `/proc/[pid]/stat` -- process status (PID, comm, state, PPID, pgrp, session, tty, starttime)
- `/proc/[pid]/status` -- effective and real UID/GID
- `/proc/[pid]/cmdline` -- full command line (for `-f` matching)
- `/proc/uptime` -- system uptime (for `--older` calculations)
- `kill()` syscall via rustix -- sends signals to matched processes
## Arguments
### Pattern
| `pattern` (positional, optional) | Extended regex to match against process names |
### Signal selection
| `--signal SIGNAL` | Signal to send, by name or number (default: TERM) |
### Output options
| `-c, --count` | Print count of matched processes instead of signaling |
| `-e, --echo` | Display name and PID of each signaled process |
### Matching options
| `-f, --full` | Match pattern against full command line, not just process name |
| `-i, --ignore-case` | Case-insensitive pattern matching |
| `-x, --exact` | Require exact match of the process name (not a substring) |
### Selection filters
| `-n, --newest` | Select only the most recently started matching process |
| `-o, --oldest` | Select only the earliest started matching process |
| `-O, --older SECS` | Select processes older than SECS seconds |
| `-P, --parent PPID,...` | Match only processes whose parent PID is listed |
| `-g, --pgroup PGRP,...` | Match only processes in the listed process groups |
| `-G, --group GID,...` | Match only processes with the listed real group IDs |
| `-s, --session SID,...` | Match only processes in the listed sessions |
| `-t, --terminal TERM,...` | Match only processes on the listed controlling terminals |
| `-u, --euid UID,...` | Match only processes with the listed effective user IDs or names |
| `-U, --uid UID,...` | Match only processes with the listed real user IDs or names |
| `-r, --runstates STATE,...` | Match only processes in the listed run states (R, S, D, Z, T, etc.) |
Note: `-v` (inverse matching) is intentionally not supported in pkill, matching
procps-ng behavior.
## Behavior
pkill iterates over all processes in `/proc`, applies the same filtering and
pattern matching logic as pgrep, then sends a signal to each matched process.
### Signal parsing
The `--signal` value is resolved in the following order:
1. Named signal without prefix: `TERM`, `HUP`, `KILL`, etc.
2. Named signal with SIG prefix: `SIGTERM`, `SIGHUP`, `SIGKILL`, etc.
3. Numeric signal: `15`, `1`, `9`, etc.
Supported signal names: HUP, INT, QUIT, ILL, TRAP, ABRT (IOT), BUS, FPE,
KILL, USR1, SEGV, USR2, PIPE, ALRM, TERM, STKFLT, CHLD (CLD), CONT, STOP,
TSTP, TTIN, TTOU, URG, XCPU, XFSZ, VTALRM, PROF, WINCH, IO (POLL), PWR, SYS.
### Process matching
The matching algorithm is shared with pgrep:
- The invoking process (pkill itself) is always excluded from matches.
- Without `-f`, the pattern is matched against the process comm name.
- With `-f`, the pattern is matched against the full command line.
- With `-x`, the pattern must match the entire name (anchored match).
- Selection filters (parent, group, terminal, etc.) are combined with AND logic.
- `-n` and `-o` are applied after all other filtering.
### Echo mode (`-e`)
When `--echo` is specified, pkill prints a line for each successfully signaled
process:
```
name killed (pid N)
```
### Count mode (`-c`)
When `--count` is specified, pkill prints the number of matching processes
instead of sending signals.
## Exit codes
| 0 | At least one process was matched and successfully signaled |
| 1 | No processes matched, or signaling failed for all matches |
| 2 | Syntax error in command line arguments |
| 3 | Fatal error |
## Divergences from procps-ng
pkill shares its matching engine with `pgrep`.
Error messages for invalid arguments use different wording.