Get Process Status ps command

Process and Service Management

When any command is run on the Linux system, a resulting process is created to carry out the requested work for that command.  Some commands start and complete so quickly they seem instant, others may start when the system is booted and run until it shuts down.

Services are processes, often started when the system starts up, that run in the background in order to provide some additional functionality.  These are often called daemons (pronounced like demon) and provide facilities such as SSH, email and automatic mounting of disks.

Examining Running Processes

The first step to managing processes is being able to identify what processes are running.  Even if the system has just been started up and nothing else, there will be dozens of processes running.  These are mostly daemons started from the init scripts at system startup.  Daemons will be covered in further detail later in this chapter.

Several attributes are tracked for each process running on the system.  When it is started, each process receives a process number to uniquely identify it on the system.  The owner and the process number of the process that starts it (the parent process) is are also tracked as well as the start time.

The ps commandis used to report the processes currently running on the system.  If no options are given, ps reports minimal information on processes owned by the current user.  To get more information, the -e and -f options may be used. The -e option requests every process and the -f option is for full information on processes listed.  These may be combined as '??ef, causing all running processes to be reported in a long output format.

$ ps -ef

UID        PID  PPID  C STIME TTY          TIME CMD
root         1     0  0 06:45 ?        00:00:12 init [3] 
root         2     1  0 06:45 ?        00:00:00 [migration/0]
root         3     1  0 06:45 ?        00:00:00 [ksoftirqd/0]
...
oracle    2718  2716  0 06:50 ?        00:00:00 sshd: oracle@pts/0
oracle    2719  2718  0 06:50 pts/0    00:00:00 -bash
root      2897  2361  0 07:14 ?        00:00:00 sshd: oracle [priv]
oracle    2899  2897  0 07:14 ?        00:00:00 sshd: oracle@pts/1
oracle    2900  2899  0 07:14 pts/1    00:00:00 -bash
oracle    2967  2900  0 07:20 pts/1    00:00:00 ps -ef


All running processes are reported, from the init process which is the first process started on the system right up to the ps command you are running to report the running processes.  There can easily be hundreds or thousands of processes running on a system, so you will typically want to restrict which processes you see.

Each line of the ps output represents a currently running process.  With the -f option, the following attributes are displayed:

Column label	Value
UID	The owner of this process
PID	The unique process ID for this process
PPID	The process ID of the parent to this process (the process that started this process)
C	The percentage of CPU time used by this process since it was started
STIME	The time (and date if before today) that this process was started
TTY	The terminal associated with this process (if any)
TIME	The total time this process has spent being processed
CMD	The command and arguments executed

There are several options to change the output format of the ps command, but for most purposes, the standard -f output is sufficient.

One way to restrict the output of the ps command is to use the -u option which causes ps to report on a specific user's processes. It is shown here with the -f option to give additional information about each process.

$ ps -fu oracle

UID        PID  PPID  C STIME TTY          TIME CMD
oracle    2718  2716  0 06:50 ?        00:00:00 sshd: oracle@pts/0
oracle    2719  2718  0 06:50 pts/0    00:00:00 -bash
oracle    2899  2897  0 07:14 ?        00:00:00 sshd: oracle@pts/1
oracle    2900  2899  0 07:14 pts/1    00:00:00 -bash
oracle    3079  2900  0 07:40 pts/1    00:00:00 -bash
oracle    3122  3079  0 07:40 pts/1    00:00:00 -bash
oracle    3172  3122  0 07:40 pts/1    00:00:00 sqlplus      
oracle    3179     1  0 07:41 ?        00:00:00 ora_pmon_TEST
oracle    3181     1  1 07:41 ?        00:00:00 ora_vktm_TEST
oracle    3185     1  0 07:41 ?        00:00:00 ora_diag_TEST
oracle    3187     1  0 07:41 ?        00:00:00 ora_dbrm_TEST
oracle    3189     1  0 07:41 ?        00:00:00 ora_psp0_TEST
oracle    3193     1  0 07:41 ?        00:00:00 ora_dia0_TEST
oracle    3195     1  1 07:41 ?        00:00:00 ora_mman_TEST
oracle    3197     1  0 07:41 ?        00:00:00 ora_dbw0_TEST
oracle    3201     1  0 07:41 ?        00:00:00 ora_lgwr_TEST
oracle    3203     1  0 07:41 ?        00:00:00 ora_ckpt_TEST
oracle    3205     1  1 07:41 ?        00:00:00 ora_smon_TEST
oracle    3207     1  0 07:41 ?        00:00:00 ora_reco_TEST
oracle    3209     1  2 07:41 ?        00:00:00 ora_mmon_TEST
oracle    3211     1  0 07:41 ?        00:00:00 ora_mmnl_TEST
oracle    3213     1  0 07:41 ?        00:00:00 ora_d000_TEST
oracle    3215     1  0 07:41 ?        00:00:00 ora_s000_TEST
oracle    3222  3172 11 07:41 ?        00:00:01 oracleTEST
(DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle    3224     1  1 07:41 ?        00:00:00 ora_fbda_TEST
oracle    3226     1  0 07:41 ?        00:00:00 ora_smco_TEST
oracle    3228     1  1 07:41 ?        00:00:00 ora_qmnc_TEST
oracle    3230     1  1 07:41 ?        00:00:00 ora_w000_TEST
oracle    3234  2719  0 07:41 pts/0    00:00:00 ps -fu oracle