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I use pgrep from procps-3.3.10.

If I have executable aout_abcdefgh_ver27, then 

pgrep aout_abcdefgh_ver27

returns nothing, while ps aux | grep aout_abcdefgh_ver27 returns the expected result:

ps aux | grep aout_abcdefgh_ver27 
evgeniy  14806  0.0  0.0   4016   672 pts/8    S    12:50   0:00 ./aout_abcdefgh_ver27
evgeniy  15241  0.0  0.0  12596  2264 pts/8    S+   12:50   0:00 grep --colour=auto aout_abcdefgh_ver27

But if I run

$ pgrep aout_abcdefgh_v
14806

pgrep returns what I expect, so I wonder why it works in such a strange way, maybe I should use some option for pgrep to work with full process name?

It looks like it has a very short limit for the pattern, something like ~ 10 symbols.

terdon
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fghj
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  • What is the command line you use to launch the process? Ideally, [edit] your question and show us the output of ps aux | grep a.out. – terdon Mar 02 '16 at 09:43
  • @terdon Thanks for comment, I update my question – fghj Mar 02 '16 at 09:54

1 Answers1

31

The problem is that by default, pgrep only searches the process name. The name is a truncated version of the entire command. You can see what the name is by looking at /proc/PID/status where PID is the process ID of the relevant process. For example:

$ ./aout_abcdefgh_ver27 &
[1] 14255                    ## this is the PID
$ grep Name /proc/14255/status
Name:   aout_abcdefgh_v

So yes, pgrep with no flags only reads the first 15 characters of the executable's name. To search the full command line used to launch it, you need the -f flag (from man pgrep):

-f, --full
     The pattern is normally only matched against the process name.  
     When -f is set, the full command line is used.

So, if you use -f:

$ pgrep -f aout_abcdefgh_ver27 
14255
terdon
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