Posts Tagged howto command line process linux
“/proc” file system
Every process has an associated sub-directory entry under “/proc” in the form “/proc/<PID>“, where <PID> is the process identifier. The “ps” command can be used to obtain the process identifier for any process by executing:
# ps aux | grep -i process_name | grep -v grep
peniwize@host:~$ ps aux | grep -i bash | grep -v grep peniwize 2255 0.0 0.1 7044 3596 pts/1 Ss 18:52 0:00 bash peniwize 2347 0.9 0.1 7044 3704 pts/2 Ss 19:08 0:00 bash
The second column is the process identifier (PID).
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
Each process sub-directory also has a read-only “cmdline” file that contains the complete command line used to execute the process. The command line arguments are separated by by nulls instead of white space, and the ‘cmdline’ files does not end with a new-line, so it is necessary to replace all nulls with spaces (or tab, or whatever you want) in order to display them. This can be done with a simple sed filter. Here are examples of the command line both raw and processed by sed:
peniwize@host:~$ cat /proc/self/cmdline && printf "\n" cat/proc/self/cmdline peniwize@host:~$ cat /proc/self/cmdline | sed 's/\x0/ /' && printf "\n" cat /proc/self/cmdline
Notice that there is no space (fourth character) between “cat” and “/proc…” in the output of the first command but there is in the output of the second. Note that most modern Linux kernels are configured to create a directory named “self” in the “/proc” file-system. “self” is an alias for the PID of the currently running process, i.e. a process can easily access “/proc/<PID>/…” by accessing “proc/self/…”.
Simple bash script to display the command line for any process by PID or by name
#!/bin/bash # # Argument 1 ($1) is the PID (or name) of the process whose command line should be shown. if [[ "$1" =~ ^[0-9]+$ ]]; then PID="$1" else PID="$(pidof $1)" fi if [[ -z "$PID" ]]; then printf "Unable to resolve process: '$1'!\n" exit 1 fi cat /proc/$PID/cmdline | sed 's/\x0/ /' && printf "\n"