Details of long running and long-forgotten processes

Sometimes we start off a new process and after quite sometime you wish to know details as to how the process was started. Things like current working directory, complete command line, environment variables used. This usually happens for the programs kicked off using a sudo-user and then you mostly quit the shell from where this was invoked. In my specific case, I was looking for the current working directory (to see where it will dump the core) and environment variables in use. In Linux, this is available in /proc/<pid>/ files.

I started browsing other entries and was amazed at the amount of useful information that is being transparently provided by Linux. Some of the notable ones are limits, statm and task. The reference link has details for other interesting details.

Here is the story:

I remember that I started the process on a particular host as the produser so log on there

> sudo -u produser ssh localhost

I remember that it is a java process - to get a handle to the process id.

> ps -ef | grep java | grep produser 
produser 8113  7983  0 02:14 pts/10   00:00:00 grep java
produser 21765 21750  0 Aug31 ?        01:46:45 /usr/local/java/jdk/bin/java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=8765,suspend=n -Dcom.sun.management.jmxremote.port=8219 -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false -classpath /tools/apache/maven/boot/classworlds-1.1.jar -Dclassworlds.conf=/tools/apache/maven/bin/m2.conf -Dmaven.home=/tools/apache/maven org.codehaus.classworlds.Launcher "--settings" "/u/produser/.m2/settings.xml" "clean" "compile" "exec:java" "-Dexec.mainClass=com.kilo.DriverCLI" "-Dexec.args=SOMETHING"

Now check the current working directory:

> ls -al /proc/21765/cwd
lrwxrwxrwx 1 produser produser 0 Oct  1 08:04 /proc/21765/cwd -> /u/produser/testproject

Now for the environment settings:

> cat /proc/21765/environ
#All environment variables were listed - elided for privacy reasons

Other interesting info:

> cat /proc/21765/limits
Limit                     Soft Limit           Hard Limit           Units
Max cpu time              unlimited            unlimited            seconds
Max file size             unlimited            unlimited            bytes
Max data size             unlimited            unlimited            bytes
Max stack size            10485760             unlimited            bytes
Max core file size        unlimited            unlimited            bytes
Max resident set          unlimited            unlimited            bytes
Max processes             16341                16341                processes
Max open files            65536                65536                files
Max locked memory         65536                65536                bytes
Max address space         unlimited            unlimited            bytes
Max file locks            unlimited            unlimited            locks
Max pending signals       256591               256591               signals
Max msgqueue size         819200               819200               bytes
Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us

> cat /proc/21765/task/21771/status
Name: java
State: S (sleeping)
Tgid: 21765
Pid: 21771
PPid: 21750
TracerPid: 0
Uid: 5307 5307 5307 5307
Gid: 5307 5307 5307 5307
Utrace: 0
FDSize: 256
Groups: 5307 6135 6584
VmPeak: 11245832 kB
VmSize: 11243768 kB
VmLck:        0 kB
VmHWM:  3575560 kB
VmRSS:  2966532 kB
VmData: 11064932 kB
VmStk:       88 kB
VmExe:        4 kB
VmLib:    15324 kB
VmPTE:     6360 kB
VmSwap:        0 kB
Threads: 31
SigQ: 0/256591
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000004
SigIgn: 0000000000000000
SigCgt: 2000000181005ccf
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
Cpus_allowed: ff
Cpus_allowed_list: 0-7
Mems_allowed: 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list: 0
voluntary_ctxt_switches: 8189
nonvoluntary_ctxt_switches: 933

References:

1. http://www.kernel.org/doc/man-pages/online/pages/man5/proc.5.html