Understanding and Using the Linux ps Command

The ps command (Process Status) lists a snapshot of the processes running on a Linux system at the moment it is executed. It is essential for monitoring and controlling processes, allowing users to see which processes are running, their states, resource usage, and more.

Command parameters:

a  显示所有进程
-a 显示同一终端下的所有程序
-A 显示所有进程
c  显示进程的真实名称
-N 反向选择
-e 等于“-A”
e  显示环境变量
f  显示程序间的关系
-H 显示树状结构
r  显示当前终端的进程
T  显示当前终端的所有程序
u  指定用户的所有进程
-au 显示较详细的资讯
-aux 显示所有包含其他使用者的行程 
-C<命令> 列出指定命令的状况
--lines<行数> 每页显示的行数
--width<字符数> 每页显示的字符数
--help 显示帮助信息
--version 显示版本显示

1. pstree

Displays processes in a tree structure.

$ pstree -p work | grep ad

sshd(22669)---bash(22670)---ad_preprocess(4551)-+-{ad_preprocess}(4552)
                                                |-{ad_preprocess}(4553)
                                                |-{ad_preprocess}(4554)
                                                |-{ad_preprocess}(4555)
                                                |-{ad_preprocess}(4556)
                                                `-{ad_preprocess}(4557)

In this example, the user work runs ad_preprocess with one main thread and six child threads.

2. ps -Lf

Shows detailed thread information.

$ ps -Lf 4551

UID        PID  PPID   LWP  C NLWP STIME TTY      STAT   TIME CMD
work      4551 22670  4551  2    7 16:30 pts/2    Sl+    0:02 ./ad_preprocess
work      4551 22670  4552  0    7 16:30 pts/2    Sl+    0:00 ./ad_preprocess
… (remaining lines omitted for brevity)

The process has launched seven threads in total.

3. pstack

Displays the stack trace of each thread in a process.

$ pstack 4551

Thread 7 (Thread 1084229984 (LWP 4552)):
#0  0x000000302afc63dc in epoll_wait () from /lib64/tls/libc.so.6
#1  0x00000000006f0730 in ub::EPollEx::poll ()
… (remaining threads omitted for brevity)

4. kill – terminating processes

Common signals for controlling processes:

kill -STOP [pid]   # send SIGSTOP to pause a process
kill -CONT [pid]   # send SIGCONT to resume a stopped process
kill -KILL [pid]   # send SIGKILL to force immediate termination
kill -9 -1          # terminate all processes you own

SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.

5. Displaying all process information

Basic commands and examples:

ps -A – list all processes.

ps -u root – show processes owned by root .

ps -ef – list all processes with full command lines.

ps -ef|grep ssh – find specific processes using grep .

ps -l – display detailed information for the current session.

ps aux – show all processes with user, CPU, memory, and other columns.

ps -axjf – display a process tree.

ps aux | egrep '(cron|syslog)' – find PIDs related to cron or syslog services.

Each command’s output columns (USER, PID, %CPU, %MEM, VSZ, RSS, TTY, STAT, START, TIME, COMMAND, etc.) are explained to help interpret the process state and resource consumption.