Find the pid of a java process under Linux

Question

I have a Java program running on a Linux computer, and want to find the process ID (pid) of its process. I know the ps command can provide this information, but its output is confusing because it has so much extraneous information. How can I get just the pid?

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I am using MPJ library in java program for Pagerank algorithm. I compile it by

javac -cp .:$MPJ_HOME/lib/mpj.jar MpiPageRank.java

and run by

mpjrun.sh -np 2 MpiPageRank

where -np is number of process

Now i have to find its pid

ps -ef|grep java

like

mpjrun.sh -np 2 MpiPageRank & sleep 2
ps -ef | grep java

I get

pnewaska 27866 27837 99 21:28 pts/45   00:00:09 java -cp /u/pnewaska/mpj-v0_38/lib/smpdev.jar:/u/pnewaska/mpj-v0_38/lib/xdev.jar:/u/pnewaska/mpj-v0_38/lib/mpjbuf.jar:/u/pnewaska/mpj-v0_38/lib/loader2.jar:/u/pnewaska/mpj-v0_38/lib/starter.jar:/u/pnewaska/mpj-v0_38/lib/mpiExp.jar runtime.starter.MulticoreStarter /nfs/nfs1/home/pnewaska/DistributedSystems/Project3 10 smpdev useLocalLoader EMPTY MpiPageRank -i input.500k0 -n 10 -o

Now I want to extract MpiPageRank from only 1 linux comman to get its pid ie 27866. how do i do that ?

Solution 1

using ps

ps allows the user to define his own formatting for its output with the -o switch, and -C to select entries by the given command. I would go with:

ps -C java -o pid

from the man page:

   -C cmdlist      Select by command name
                   This selects the processes whose executable name is given in cmdlist.

   -o format       user-defined format.
                   format is a single argument in the form of a blank-separated or comma-separated list, which offers a way to specify
                   individual output columns. The recognized keywords are described in the STANDARD FORMAT SPECIFIERS section below. Headers
                   may be renamed (ps -o pid,ruser=RealUser -o comm=Command) as desired. If all column headers are empty
                   (ps -o pid= -o comm=) then the header line will not be output. Column width will increase as needed for wide headers; this
                   may be used to widen up columns such as WCHAN (ps -o pid,wchan=WIDE-WCHAN-COLUMN -o comm). Explicit width control
                   (ps opid,wchan:42,cmd) is offered too. The behavior of ps -o pid=X,comm=Y varies with personality; output may be one
                   column named "X,comm=Y" or two columns named "X" and "Y". Use multiple -o options when in doubt. Use the PS_FORMAT
                   environment variable to specify a default as desired; DefSysV and DefBSD are macros that may be used to choose the default
                   UNIX or BSD columns.

One can get more accurate results by specifying more restrictions (ie the user under which the process runs, etc). Look at the man page for more information and other switches.

example:

$ sleep 10 &
[1] 12654
$ ps -C sleep -o pid
12654

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using the shell

I don't know why you use an .sh script to run your code and not call java directly, but if in any case you use the & (background) operator, you can grab the pid through your shell, with the $! variable.

for example:

$ sleep 5 &
[1] 12395
$ echo $!
12395

same goes for the java -jar .. & command, $! will be set to the pid of the last backgrounded job.

Solution 2

You can use awk to get the pid:

ps -ef | grep MpiPageRank | awk '{print $2}'

I noticed that sometimes grep itself gets found, to remove it:

ps -ef | grep MpiPageRank | grep -v grep | awk '{print $2}'

Solution 3

jps is the same as ps except it only looks at java processes.

If you then need the PID, you can do something like the following:

jps | grep JAVA_NAME | awk '{print $1}'

That runs jps, then uses grep to filter by the java application or jar you want to kill. After that, awk captures and prints just the pid to the console.

Solution 4

A simple way is to run this:

pgrep java

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