> ## Documentation Index > Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt > Use this file to discover all available pages before exploring further. # Create Monitor and Kill Processes > This article explains how to create, monitor, and manage processes in Linux using various commands and techniques. Understanding how to manage processes is fundamental for any Linux administrator. A process is simply a running instance of a program, from short-lived commands like `ls` to long-running services. ## 1. Launching a Process For example, running: ```bash theme={null} [aaron@LFCS-CentOS ~]$ ls absolute_picture_shortcut all_output.txt archive.tar archive.zip Desktop Documents Downloads file1 file1.gz file2 file2.bz2 file3 file3.xz fstab_shortcut Music nomachine_7.7.4_1_x86_64.rpm Pictures Public shortcut_to_directory script.sh Templates testfile videos [aaron@LFCS-CentOS ~]$ ``` creates a short-lived `ls` process that exits once the directory contents are shown. *** ## 2. Inspecting Processes with `ps` The `ps` command lists active processes. It has two distinct option styles: | Syntax Style | Example | Description | | ------------ | -------- | ------------------------------------- | | UNIX-style | `ps -e` | Show every process | | BSD-style | `ps axu` | All processes in user-oriented format | To view all processes in a user-friendly layout, combine `a` (others’ processes), `x` (no controlling terminal), and `u` (user format): ```bash theme={null} ps aux ``` ```text theme={null} USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.3 241296 14000 ? Ss Mar23 0:01 /usr/lib/systemd/systemd aaron 6601 6.2 4.8 3142460 185096 ? S 10:27 0:06 gnome-shell … more … ``` ### 2.1 Exploring `ps` Options ![The image shows a terminal window displaying the manual page for the ps command, which reports a snapshot of current processes. It includes sections like NAME, SYNOPSIS, and DESCRIPTION, explaining the command's usage and options.](https://kodekloud.com/kk-media/image/upload/v1752881389/notes-assets/images/Linux-Professional-Institute-LPIC-1-Exam-101-Create-Monitor-and-Kill-Processes/ps-command-manual-terminal-snapshot.jpg) Common invocations from the manual: * **Full format** ```bash theme={null} ps -ef # UNIX full format ps axu # BSD with user columns ``` * **Process tree** ```bash theme={null} ps -ejH ps axjf ``` * **Thread details** ```bash theme={null} ps -Elf ps axms ``` ### 2.2 Understanding `ps aux` Columns | Column | Description | | ------- | ------------------------ | | USER | Process owner | | PID | Process ID | | %CPU | CPU usage at sample time | | %MEM | Physical memory usage | | VSZ | Virtual memory size (KB) | | RSS | Resident Set Size (KB) | | STAT | Process state | | START | Start time or date | | TIME | Cumulative CPU time | | COMMAND | Command with arguments | Kernel threads run in kernel space and appear in square brackets, e.g., `[kworker/0:1]`. *** ## 3. Real-Time Monitoring with `top` To watch processes live: ```bash theme={null} top ``` ```text theme={null} top - 10:15:42 up 2:31, 1 user, load average: 0.01, 0.05, 0.03 Tasks: 236 total, 1 running, 235 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.5 us, 0.2 sy, 99.3 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st MiB Mem : 3731.4 total, 1588.9 free, 915.6 used, 1227.1 buff/cache MiB Swap: 2048.0 total, 2048.0 free, 0.0 used. 2554.1 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 6601 aaron 20 0 3142460 185096 104268 S 6.2 4.8 00:06.60 gnome-shell 1 root 20 0 241296 14000 8912 S 0.0 0.4 00:01.26 systemd … ``` * Use arrow keys or Page Up/Page Down to navigate. * Press `Q` to quit. *** ## 4. Targeted Process Listings | Task | Command | | ---------------------- | ------------------------- | | By PID | `ps -p 1` or `ps -p 1 -u` | | By user | `ps -u aaron` | | By name (with `pgrep`) | `pgrep -a syslog` | ```bash theme={null} # Find syslog processes: pgrep -a syslog # Kill them: pkill -KILL syslog ``` *** ## 5. Managing Process Priority (Niceness) Niceness spans **-20** (highest priority) to **19** (lowest). Lower niceness → higher scheduling priority. ### 5.1 Launching with `nice` ```bash theme={null} nice -n 11 bash ``` ### 5.2 Viewing Niceness ```bash theme={null} ps -l | head -n 6 F UID PID PPID PRI NI VSZ RSS WCHAN STAT COMMAND … 0 1000 6543 6540 20 0 658840 19268 – SL+ /usr/bin/gnome-shell 4 1000 6673 6669 20 11 302924 8516 – Sl bash ``` The **NI** column shows the niceness value. ### 5.3 Changing with `renice` ```bash theme={null} # Increase niceness (lower priority): renice 15 6673 # Decrease niceness (requires sudo): sudo renice -5 6673 ``` *** ## 6. Signals and `kill` Linux uses signals to control processes: | Signal | Number | Description | | ------- | ------ | ------------------------ | | SIGHUP | 1 | Hangup/reload | | SIGINT | 2 | Interrupt (Ctrl+C) | | SIGTERM | 15 | Graceful shutdown | | SIGKILL | 9 | Force kill (uncatchable) | ```bash theme={null} # List all signal names and numbers: kill -l ``` You can omit the `SIG` prefix: ```bash theme={null} kill -s KILL 1234 kill -9 1234 kill 1234 # defaults to SIGTERM ``` Using `SIGKILL` (`kill -9`) does not allow cleanup and may leave resources in an inconsistent state. Use `SIGTERM` first. ### Example: Restarting `sshd` ```bash theme={null} systemctl status sshd.service sudo kill -SIGHUP 1147 systemctl status sshd.service # sshd[1147]: Received SIGHUP; restarting. ``` *** ## 7. Shell Job Control | Action | Keystroke or Command | | ----------------------- | -------------------- | | Interrupt (SIGINT) | Ctrl+C | | Pause/Stop (SIGTSTP) | Ctrl+Z | | Background a command | `sleep 180 &` | | List jobs | `jobs` | | Bring job to foreground | `fg %1` | | Resume in background | `bg %1` | *** ## 8. Open Files with `lsof` * List files opened by a PID: ```bash theme={null} lsof -p 8401 ``` * Find which process holds a file: ```bash theme={null} sudo lsof /var/log/messages ``` Use `sudo` when required to avoid permission denied errors. *** That concludes our guide on creating, monitoring, and killing processes in Linux. Practice these commands in a lab environment to master process management. ## Links and References * [ps(1) — Linux Manual Page](https://man7.org/linux/man-pages/man1/ps.1.html) * [top(1) — Linux Manual Page](https://man7.org/linux/man-pages/man1/top.1.html) * [kill(1) — Linux Manual Page](https://man7.org/linux/man-pages/man1/kill.1.html) * [lsof(8) — Linux Manual Page](https://linux.die.net/man/8/lsof)