Memory Usage – How to Find Which Processes Are Taking All the Memory

You can use tstime to measure the highwater memory usage (RSS and virtual) of a process.

For example:

$ tstime date       
Tue Aug 16 21:35:02 CEST 2011

Exit status: 0

pid: 31169 (date) started: Tue Aug 16 21:35:02 2011
        real   0.017 s, user   0.000 s, sys   0.000s
        rss      888 kb, vm     9764 kb

It also supports a more easy to parse output mode (-t).

NOTE: Assuming you have this version of top (procps). You can check with this command:

$ top --version
    top: procps version 3.2.8
usage:  top -hv | -bcisSH -d delay -n iterations [-u user | -U user] -p pid [,pid ...]

procps is often the version of top included with Fedora/CentOS/RHEL and other variants.

Changing columns

If you look in the man page for top you'll see a section titled: "2b. SELECTING and ORDERING Columns". There are keyboard shortcuts for toggling visibility for the different fields/columns.

For example:

  f,o     . Fields/Columns: 'f' add or remove; 'o' change display order
  F or O  . Select sort field
  <,>     . Move sort field: '<' next col left; '>' next col right

You can use the key f while in top to get to a secondary screen where you can specify which columns should be toggled visible or not:

For example:

Current Fields:  ANOPQRSTUVbcdefgjlmyzWHIKX  for window 3:Mem
Toggle fields via field letter, type any other key to return 

* A: PID        = Process Id                                      * W: S          = Process Status
* N: %MEM       = Memory usage (RES)                              * H: PR         = Priority
* O: VIRT       = Virtual Image (kb)                              * I: NI         = Nice value
* P: SWAP       = Swapped size (kb)                               * K: %CPU       = CPU usage
* Q: RES        = Resident size (kb)                              * X: COMMAND    = Command name/line
* R: CODE       = Code size (kb)
...

There are more, these are just a sample. When you're done toggling the columns the way you want, use the Esc to get out of the selection screen.

Saving configuration

You can use the Shift+W to save your changes so they're the defaults:

  W         Write configuration file

The file is stored here, $HOME/.toprc, and looks like this:

$ more .toprc 
RCfile for "top with windows"       # shameless braggin'
Id:a, Mode_altscr=0, Mode_irixps=1, Delay_time=1.000, Curwin=2
Def fieldscur=AEHIoqTWKNMBcdfgjpLrsuvyzX
    winflags=129016, sortindx=19, maxtasks=0
    summclr=2, msgsclr=5, headclr=7, taskclr=7
Job fieldscur=ABcefgjlrstuvyzMKNHIWOPQDX
    winflags=63416, sortindx=13, maxtasks=0
    summclr=6, msgsclr=6, headclr=7, taskclr=6
Mem fieldscur=ANOPQRSTUVbcdefgjlmyzWHIKX
    winflags=65464, sortindx=13, maxtasks=0
    summclr=5, msgsclr=5, headclr=4, taskclr=5
Usr fieldscur=ABDECGfhijlopqrstuvyzMKNWX
    winflags=65464, sortindx=12, maxtasks=0
    summclr=3, msgsclr=3, headclr=2, taskclr=7

See section 5 of the man page for more details, "5. FILES".