Swap Space

I have a CentOS 6.7 64 bit machine having 64GB RAM. When running free command it shows that it is using about 1420 MB of Swap space. My question is how to know which process is using Swap?

# free -m
             total       used       free     shared    buffers     cached
Mem:         64410      60119       4291      14534        426      56235
-/+ buffers/cache:       3456      60953 
Swap:        32271       1420      30851 

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Since the machine has good enough RAM I don't think it should need to use Swap.
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andreasSystem AdminCommented:
yum install smem



will show you the processes and how much swap they are using.
Shiju JacobInfo Security ManagerCommented:

try using this script

# Get current swap usage for all running processes
# Erik Ljungstrom 27/05/2011
for DIR in `find /proc/ -maxdepth 1 -type d | egrep "^/proc/[0-9]"` ; do
        PID=`echo $DIR | cut -d / -f 3`
        PROGNAME=`ps -p $PID -o comm --no-headers`
        for SWAP in `grep Swap $DIR/smaps 2>/dev/null| awk '{ print $2 }'`
                let SUM=$SUM+$SWAP
        echo "PID=$PID - Swap used: $SUM - ($PROGNAME )"

echo "Overall swap used: $OVERALL"

sh new.sh | sort -n -k 5
sysautomationAuthor Commented:
Thanks to both of you. Both the solutions show 0 MB swap usage:

# smem
  PID User     Command                         Swap      USS      PSS      RSS 

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But free is still showing 1420 MB.

Any idea why?
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andreasSystem AdminCommented:
Any tmpfs filesystems on your machine? They will also eat up swap.

you can check with
if there are any tmpfs.

With df -k you can check how big they are and how much of it is used.

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sysautomationAuthor Commented:
Yes it has tmpfs:

Filesystem            Size  Used Avail Use% Mounted on
                       50G  3.6G   44G   8% /
tmpfs                  32G   16G   16G  50% /dev/shm
/dev/sda1             477M   64M  388M  15% /boot
                      689G  107G  548G  17% /home
                      886G  236G  606G  29% /opt

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But it is saying 16GB used whereas free saying 1420MB use. Why are they different?
andreasSystem AdminCommented:
Maybe only parts of /dev/shm are kept in swap and the rest in memory cache?

But this is just a guess I'm not sure.

But you shouldnt be worfried about your system uses some swap even it has enough memory.

Ressources in swap on systems with a lot of memory are things that were not accessed in a long time. You may adjust the swappiness parameter of the kernel to adjust the swap behaviour of your machine.

more about how to do this here: https://www.howtoforge.com/tutorial/linux-swappiness/
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