> ## 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. # Diagnose and manage processes > This article explains how to diagnose and manage processes in Linux for effective system administration. When you start any application, Linux creates a *process* that runs until completion or termination. Understanding how to monitor and control these processes is essential for effective system administration and performance tuning. ## Short-Lived vs. Long-Lived Processes ### Short-Lived Processes Commands like `ls` spawn a process that exits immediately after running: ```bash theme={null} $ ls absolute_picture_shortcut all_output.txt archive.zip archive.tar Desktop Documents … $ # Process ends when directory listing is complete ``` ### Long-Lived Processes Daemons such as `sshd` or long-running services remain active until explicitly stopped. To inspect active processes, the `ps` command is your first stop. *** ## Inspecting Processes with `ps` `ps` provides a snapshot of processes. It supports two option syntaxes: | Syntax Style | Example | Description | | ------------ | -------- | ------------------------------------- | | Unix (POSIX) | `ps -e` | Standard options prefixed with a dash | | BSD | `ps axu` | Options without a dash | Use `man ps` to explore all options and compare Unix vs. BSD syntax. ### Common `ps` Usage * Show processes in the current terminal: ```bash theme={null} $ ps PID TTY TIME CMD 7726 pts/0 00:00:00 bash 7796 pts/0 00:00:00 ps ``` * List **all** system processes in user-oriented format: ```bash theme={null} $ ps aux 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 7726 0.0 0.4 3142460 185096 pts/0 S+ 10:00 0:00 gnome-system-monitor … ``` The mnemonic **aux** (a: all with terminal, u: user format, x: include daemons) helps recall this combination. ![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.](https://kodekloud.com/kk-media/image/upload/v1752881489/notes-assets/images/Linux-System-Administration-for-Beginners-Diagnose-and-manage-processes/ps-command-manual-terminal-snapshot.jpg) Excerpt from `man ps`: ```text theme={null} To see every process on the system using standard syntax: ps -e ps -ef Using BSD syntax: ps ax ps axu To print a process tree: ps -ejH ps axjf ``` *** ## Real-Time Monitoring with `top` For continuous updates: ```bash theme={null} $ top top - 10:15:03 up 1 day, 2:34, 1 user, load average: 0.05, 0.03, 0.01 Tasks: 236 total, 1 running, 235 sleeping %Cpu(s): 1.2 us, 0.5 sy, 98.3 id MiB Mem : 3731.4 total, 1588.9 free, 915.5 used, 1227.0 buff/cache PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 6601 aaron 20 0 3142460 185096 104268 S 6.2 4.8 0:06.60 gnome-shell 1 root 20 0 241296 14000 8912 S 0.0 0.4 0:01.26 systemd … ``` * Use Up/Down arrows or `Page Up`/`Page Down` to scroll. * Press `q` to exit. *** ## Filtering Processes | Filter Type | Command Example | | ----------- | -------------------------------------- | | By PID | `ps -p 1 -o pid,tty,stat,time,command` | | By User | `ps -U aaron -u` | | By Name | `pgrep -a syslog` | ```bash theme={null} $ pgrep -a syslog 1455 /usr/sbin/rsyslogd -n ``` *** ## Adjusting Niceness (Priority) Process priority (`nice` value) ranges from **–20** (highest) to **+19** (lowest). * Launch with niceness 11: ```bash theme={null} $ nice -n 11 bash ``` * View niceness: ```bash theme={null} $ ps -l F UID PID PPID PRI NI VSZ RSS STAT TTY TIME COMMAND 0 1000 6543 6540 20 11 658840 19268 S+ tty2 0:00 bash ``` * Change niceness of an existing PID: ```bash theme={null} $ sudo renice 7 6543 6543 (process ID) old priority 11, new priority 7 ``` *** ## Parent/Child Process Trees Display processes as a hierarchy: ```bash theme={null} $ ps faxu ``` ![The image shows a terminal window displaying a list of running processes on a CentOS system, including details like user, PID, CPU and memory usage, and command paths.](https://kodekloud.com/kk-media/image/upload/v1752881490/notes-assets/images/Linux-System-Administration-for-Beginners-Diagnose-and-manage-processes/centos-terminal-running-processes-list.jpg) *** ## Sending Signals Linux signals control process behavior. Common signals include: | Signal | Number | Default Action | | ------- | ------ | ---------------------- | | SIGHUP | 1 | Hangup (reload config) | | SIGINT | 2 | Interrupt | | SIGTERM | 15 | Graceful termination | | SIGKILL | 9 | Force kill | | SIGSTOP | 19 | Pause | | SIGCONT | 18 | Continue | List all signals: ```bash theme={null} $ kill -l 1) SIGHUP 2) SIGINT 3) SIGQUIT 9) SIGKILL 15) SIGTERM 18) SIGCONT 19) SIGSTOP ``` Examples: ```bash theme={null} # Reload sshd configuration $ sudo kill -SIGHUP # Graceful shutdown $ kill # Force kill $ kill -9 # Kill by name $ pkill -KILL bash ``` Killing your login shell (e.g., `bash`) will close your terminal or SSH session. *** ## Job Control: Background & Foreground * **Ctrl+C**: Interrupt * **Ctrl+Z**: Suspend ```bash theme={null} $ vim /etc/hostname [1]+ Stopped vim /etc/hostname $ fg vim /etc/hostname ``` * Start in background: `sleep 300 &` * List jobs: `jobs` * Bring to foreground: `fg %1` * Send to background: `bg %1` *** ## Inspecting Open Files with `lsof` List files held by a process: ```bash theme={null} $ lsof -p $(pgrep -n bash) COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME bash 8401 aaron cwd DIR 253,0 4096 262658 /home/aaron bash 8401 aaron txt REG 253,0 925360 514014 /usr/bin/bash … ``` View root-owned processes: ```bash theme={null} $ sudo lsof -p 1 ``` Find processes using a specific file: ```bash theme={null} $ sudo lsof /var/log/messages ``` *** ## Links and References * [ps(1) Manual](https://man7.org/linux/man-pages/man1/ps.1.html) * [top(1) Manual](https://man7.org/linux/man-pages/man1/top.1.html) * [kill(1) Manual](https://man7.org/linux/man-pages/man1/kill.1.html) * [lsof(8) Manual](https://man7.org/linux/man-pages/man8/lsof.8.html) * [Linux Process Management Guide](https://linux.die.net/man/1/ps)