What is a long killer?

Long Killer is a user script in Unix/Linux systems designed to find and forcibly terminate processes running longer than a specified time. It is commonly used for resource management and preventing system hangs. It can be implemented in various scripting languages such as Bash or Python.

Working principle:

1. Determining the list of running processes (e.g., using ps).
2. Filtering processes based on various criteria (user, command name, etc.).
3. Determining the runtime of each relevant process.
4. Comparing the runtime with a predefined threshold.
5. Sending a termination signal (e.g., SIGTERM or SIGKILL) to processes that exceed the threshold.

Example implementation in Bash:

#!/bin/bash

# Threshold time in seconds
THRESHOLD_SECONDS=3600 # 1 hour

# Name of the process to search for. Leave empty '' to search all processes of the user
PROCESS_NAME=""

# User under whose account the processes are running. Leave empty '' to search processes of all users
USER=""

# Exclude processes by name (space-separated)
EXCLUDE_PROCESSES="sshd bash long_killer.sh"

# Get list of processes, their runtime (ET), PID, command name, and user
ps -eo etime,pid,cmd,user --no-headers | while read ET PID CMD USER_NAME; do
    # Convert runtime to seconds
    SECS=0
    if [[ "$ET" =~ ([0-9]+)-([0-9]+):([0-9]+):([0-9]+) ]]; then # Days-hours:minutes:seconds
        SECS=$(( ${BASH_REMATCH[1]}*86400 + ${BASH_REMATCH[2]}*3600 + ${BASH_REMATCH[3]}*60 + ${BASH_REMATCH[4]} ))
    elif [[ "$ET" =~ ([0-9]+):([0-9]+):([0-9]+) ]]; then # Hours:minutes:seconds
        SECS=$(( ${BASH_REMATCH[1]}*3600 + ${BASH_REMATCH[2]}*60 + ${BASH_REMATCH[3]} ))
    elif [[ "$ET" =~ ([0-9]+):([0-9]+) ]]; then # Minutes:seconds
        SECS=$(( ${BASH_REMATCH[1]}*60 + ${BASH_REMATCH[2]} ))
    elif [[ "$ET" =~ ([0-9]+) ]]; then # Seconds
        SECS=${BASH_REMATCH[1]}
    fi

    # Check conditions for termination
    KILL=false
    if [ "$SECS" -gt "$THRESHOLD_SECONDS" ]; then
        KILL=true
    fi

    if [ -n "$PROCESS_NAME" ] && [[ ! "$CMD" =~ "$PROCESS_NAME" ]]; then
        KILL=false
    fi

    if [ -n "$USER" ] && [ "$USER_NAME" != "$USER" ]; then
        KILL=false
    fi

    # Check exclusion list
    for EXCLUDE in $EXCLUDE_PROCESSES; do
        if [[ "$CMD" == *"$EXCLUDE"* ]]; then
            KILL=false
            break
        fi
    done

    # Terminate process if all conditions are met and it's not the current script
    if [ "$KILL" = true ] && [ "$PID" != "$$" ]; then
        echo "Killing process $PID ($CMD) running for $ET"
        kill $PID # You can use kill -9 $PID for forceful termination
    fi
done

This script can be scheduled to run periodically, for example, via Crontab.

# Run every minute
* * * * * /path/to/your/long_killer.sh >> /var/log/long_killer.log 2>&1

It is important to carefully set the criteria and thresholds to avoid unintentional termination of critical system processes.