What does the SWAP column in top command stand for? [duplicate] - linux

Question

Under Linux, how do I find out which process is using the swap space more?

Answer 1

The best script I found is on this page : http://northernmost.org/blog/find-out-what-is-using-your-swap/
Here's one variant of the script and no root needed:
#!/bin/bash
# Get current swap usage for all running processes
# Erik Ljungstrom 27/05/2011
# Modified by Mikko Rantalainen 2012-08-09
# Pipe the output to "sort -nk3" to get sorted output
# Modified by Marc Methot 2014-09-18
# removed the need for sudo
SUM=0
OVERALL=0
for DIR in `find /proc/ -maxdepth 1 -type d -regex "^/proc/[0-9]+"`
do
PID=`echo $DIR | cut -d / -f 3`
PROGNAME=`ps -p $PID -o comm --no-headers`
for SWAP in `grep VmSwap $DIR/status 2>/dev/null | awk '{ print $2 }'`
do
let SUM=$SUM+$SWAP
done
if (( $SUM > 0 )); then
echo "PID=$PID swapped $SUM KB ($PROGNAME)"
fi
let OVERALL=$OVERALL+$SUM
SUM=0
done
echo "Overall swap used: $OVERALL KB"

Answer 2

Run top then press OpEnter. Now processes should be sorted by their swap usage.
Here is an update as my original answer does not provide an exact answer to the problem as pointed out in the comments. From the htop FAQ:
It is not possible to get the exact size of used swap space of a
process. Top fakes this information by making SWAP = VIRT - RES, but
that is not a good metric, because other stuff such as video memory
counts on VIRT as well (for example: top says my X process is using
81M of swap, but it also reports my system as a whole is using only 2M
of swap. Therefore, I will not add a similar Swap column to htop
because I don't know a reliable way to get this information (actually,
I don't think it's possible to get an exact number, because of shared
pages).

Answer 3

Here's another variant of the script, but meant to give more readable output (you need to run this as root to get exact results):
#!/bin/bash
# find-out-what-is-using-your-swap.sh
# -- Get current swap usage for all running processes
# --
# -- rev.0.3, 2012-09-03, Jan Smid - alignment and intendation, sorting
# -- rev.0.2, 2012-08-09, Mikko Rantalainen - pipe the output to "sort -nk3" to get sorted output
# -- rev.0.1, 2011-05-27, Erik Ljungstrom - initial version
SCRIPT_NAME=`basename $0`;
SORT="kb"; # {pid|kB|name} as first parameter, [default: kb]
[ "$1" != "" ] && { SORT="$1"; }
[ ! -x `which mktemp` ] && { echo "ERROR: mktemp is not available!"; exit; }
MKTEMP=`which mktemp`;
TMP=`${MKTEMP} -d`;
[ ! -d "${TMP}" ] && { echo "ERROR: unable to create temp dir!"; exit; }
>${TMP}/${SCRIPT_NAME}.pid;
>${TMP}/${SCRIPT_NAME}.kb;
>${TMP}/${SCRIPT_NAME}.name;
SUM=0;
OVERALL=0;
echo "${OVERALL}" > ${TMP}/${SCRIPT_NAME}.overal;
for DIR in `find /proc/ -maxdepth 1 -type d -regex "^/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 $2 }'`
do
let SUM=$SUM+$SWAP
done
if (( $SUM > 0 ));
then
echo -n ".";
echo -e "${PID}\t${SUM}\t${PROGNAME}" >> ${TMP}/${SCRIPT_NAME}.pid;
echo -e "${SUM}\t${PID}\t${PROGNAME}" >> ${TMP}/${SCRIPT_NAME}.kb;
echo -e "${PROGNAME}\t${SUM}\t${PID}" >> ${TMP}/${SCRIPT_NAME}.name;
fi
let OVERALL=$OVERALL+$SUM
SUM=0
done
echo "${OVERALL}" > ${TMP}/${SCRIPT_NAME}.overal;
echo;
echo "Overall swap used: ${OVERALL} kB";
echo "========================================";
case "${SORT}" in
name )
echo -e "name\tkB\tpid";
echo "========================================";
cat ${TMP}/${SCRIPT_NAME}.name|sort -r;
;;
kb )
echo -e "kB\tpid\tname";
echo "========================================";
cat ${TMP}/${SCRIPT_NAME}.kb|sort -rh;
;;
pid | * )
echo -e "pid\tkB\tname";
echo "========================================";
cat ${TMP}/${SCRIPT_NAME}.pid|sort -rh;
;;
esac
rm -fR "${TMP}/";

Answer 4

Use smem
smem -s swap -r
Here is a link which tells you both how to install it and how to use it: http://www.cyberciti.biz/faq/linux-which-process-is-using-swap/

Answer 5

It's not entirely clear if you mean you want to find the process who has most pages swapped out or process who caused most pages to be swapped out.
For the first you may run top and order by swap (press 'Op'), for the latter you can run vmstat and look for non-zero entries for 'so'.

Answer 6

Another script variant avoiding the loop in shell:
#!/bin/bash
grep VmSwap /proc/[0-9]*/status | awk -F':' -v sort="$1" '
{
split($1,pid,"/") # Split first field on /
split($3,swp," ") # Split third field on space
cmdlinefile = "/proc/"pid[3]"/cmdline" # Build the cmdline filepath
getline pname[pid[3]] < cmdlinefile # Get the command line from pid
swap[pid[3]] = sprintf("%6i %s",swp[1],swp[2]) # Store the swap used (with unit to avoid rebuilding at print)
sum+=swp[1] # Sum the swap
}
END {
OFS="\t" # Change the output separator to tabulation
print "Pid","Swap used","Command line" # Print header
if(sort) {
getline max_pid < "/proc/sys/kernel/pid_max"
for(p=1;p<=max_pid;p++) {
if(p in pname) print p,swap[p],pname[p] # print the values
}
} else {
for(p in pname) { # Loop over all pids found
print p,swap[p],pname[p] # print the values
}
}
print "Total swap used:",sum # print the sum
}'
Standard usage is script.sh to get the usage per program with random order (down to how awk stores its hashes) or script.sh 1 to sort the output by pid.
I hope I've commented the code enough to tell what it does.

Answer 7

Yet two more variants:
Because top or htop could be not installed on small systems, browsing /proc stay always possible.
Even on small systems, you will found a shell...
A shell variant! (Not bash only)
This is exactly same than lolotux script, but without any fork to grep, awk or ps. This is a lot quicker!
And as bash is one of the poorest shell regarding performance, a little work was done to ensure this script will run well under dash, busybox and some other. Then, (thanks to Stéphane Chazelas,) become a lot quicker again!
#!/bin/sh
# Get current swap usage for all running processes
# Felix Hauri 2016-08-05
# Rewritted without fork. Inspired by first stuff from
# Erik Ljungstrom 27/05/2011
# Modified by Mikko Rantalainen 2012-08-09
# Pipe the output to "sort -nk3" to get sorted output
# Modified by Marc Methot 2014-09-18
# removed the need for sudo
OVERALL=0
for FILE in /proc/[0-9]*/status ;do
SUM=0
while read FIELD VALUE;do
case $FIELD in
Pid ) PID=$VALUE ;;
Name ) PROGNAME="$VALUE" ;;
VmSwap ) SUM=${VALUE%% *} ; break ;;
esac
done <$FILE
[ $SUM -gt 0 ] &&
printf "PID: %9d swapped: %11d KB (%s)\n" $PID $SUM "$PROGNAME"
OVERALL=$((OVERALL+SUM))
done
printf "Total swapped memory: %14u KB\n" $OVERALL
Don't forgot to double quote "$PROGNAME" ! See Stéphane Chazelas's comment:
read FIELD PROGNAME < <(
perl -ne 'BEGIN{$0="/*/*/../../*/*"} print if /^Name/' /proc/self/status
)
echo $FIELD "$PROGNAME"
Don't try echo $PROGNAME without double quote on sensible system, and be ready to kill current shell before!
And a perl version
As this become a not so simple script, time is comming to write a dedicated tool by using more efficient language.
#!/usr/bin/perl -w
use strict;
use Getopt::Std;
my ($tot,$mtot)=(0,0);
my %procs;
my %opts;
getopt('', \%opts);
sub sortres {
return $a <=> $b if $opts{'p'};
return $procs{$a}->{'cmd'} cmp $procs{$b}->{'cmd'} if $opts{'c'};
return $procs{$a}->{'mswap'} <=> $procs{$b}->{'mswap'} if $opts{'m'};
return $procs{$a}->{'swap'} <=> $procs{$b}->{'swap'};
};
opendir my $dh,"/proc";
for my $pid (grep {/^\d+$/} readdir $dh) {
if (open my $fh,"</proc/$pid/status") {
my ($sum,$nam)=(0,"");
while (<$fh>) {
$sum+=$1 if /^VmSwap:\s+(\d+)\s/;
$nam=$1 if /^Name:\s+(\S+)/;
}
if ($sum) {
$tot+=$sum;
$procs{$pid}->{'swap'}=$sum;
$procs{$pid}->{'cmd'}=$nam;
close $fh;
if (open my $fh,"</proc/$pid/smaps") {
$sum=0;
while (<$fh>) {
$sum+=$1 if /^Swap:\s+(\d+)\s/;
};
};
$mtot+=$sum;
$procs{$pid}->{'mswap'}=$sum;
} else { close $fh; };
};
};
map {
printf "PID: %9d swapped: %11d (%11d) KB (%s)\n",
$_, $procs{$_}->{'swap'}, $procs{$_}->{'mswap'}, $procs{$_}->{'cmd'};
} sort sortres keys %procs;
printf "Total swapped memory: %14u (%11u) KB\n", $tot,$mtot;
could by run with one of
-c sort by command name
-p sort by pid
-m sort by swap values
by default, output is sorted by status's vmsize

Answer 8

The top command also contains a field to display the number of page faults for a process. The process with maximum page faults would be the process which is swapping most.
For long running daemons it might be that they incur large number of page faults at the beginning and the number does not increase later on. So we need to observe whether the page faults is increasing.

Answer 9

I adapted a different script on the web to this long one-liner:
{ date;for f in /proc/[0-9]*/status; do
awk '{k[$1]=$2} END { if (k["VmSwap:"]) print k["Pid:"],k["Name:"],k["VmSwap:"];}' $f 2>/dev/null;
done | sort -n ; }
Which I then throw into a cronjob and redirect output to a logfile. The information here is the same as accumulating the Swap: entries in the smaps file, but if you want to be sure, you can use:
{ date;for m in /proc/*/smaps;do
awk '/^Swap/ {s+=$2} END { if (s) print FILENAME,s }' $m 2>/dev/null;
done | tr -dc ' [0-9]\n' |sort -k 1n; }
The output of this version is in two columns: pid, swap amount. In the above version, the tr strips the non-numeric components. In both cases, the output is sorted numerically by pid.

Answer 10

Gives totals and percentages for process using swap
smem -t -p
Source : https://www.cyberciti.biz/faq/linux-which-process-is-using-swap/

Answer 11

On MacOSX, you run top command as well but need to type "o" then "vsize" then ENTER.

Answer 12

Since the year 2015 kernel patch that adds SwapPss (https://lore.kernel.org/patchwork/patch/570506/) one can finally get proportional swap count meaning that if a process has swapped a lot and then it forks, both forked processes will be reported to swap 50% each. And if either then forks, each process is counted 33% of the swapped pages so if you count all those swap usages together, you get real swap usage instead of value multiplied by process count.
In short:
(cd /proc; for pid in [0-9]*; do printf "%5s %6s %s\n" "$pid" "$(awk 'BEGIN{sum=0} /SwapPss:/{sum+=$2} END{print sum}' $pid/smaps)" "$(cat $pid/comm)"; done | sort -k2n,2 -k1n,1)
First column is pid, second column is swap usage in KiB and rest of the line is command being executed. Identical swap counts are sorted by pid.
Above may emit lines such as
awk: cmd. line:1: fatal: cannot open file `15407/smaps' for reading (No such file or directory)
which simply means that process with pid 15407 ended between seeing it in the list for /proc/ and reading the process smaps file. If that matters to you, simply add 2>/dev/null to the end. Note that you'll potentially lose any other possible diagnostics as well.
In real world example case, this changes other tools reporting ~40 MB swap usage for each apache child running on one server to actual usage of between 7-3630 KB really used per child.

Answer 13

That is my one liner:
cat /proc/*/status | grep -E 'VmSwap:|Name:' | grep VmSwap -B1 | cut -d':' -f2 | grep -v '\-\-' | grep -o -E '[a-zA-Z0-9]+.*$' | cut -d' ' -f1 | xargs -n2 echo | sort -k2 -n
The steps in this line are:
Get all the data in /proc/process/status for all processes
Select the fields VmSwap and Name for each
Remove the processes that don't have the VmSwap field
Remove the names of the fields (VmSwap: and Name:)
Remove lines with -- that were added by the previous step
Remove the spaces at the start of the lines
Remove the second part of each process name and " kB" after the swap usage number
Take name and number (process name and swap usage) and put them in one line, one after the other
Sort the lines by the swap usage

Answer 14

I suppose you could get a good guess by running top and looking for active processes using a lot of memory. Doing this programatically is harder---just look at the endless debates about the Linux OOM killer heuristics.
Swapping is a function of having more memory in active use than is installed, so it is usually hard to blame it on a single process. If it is an ongoing problem, the best solution is to install more memory, or make other systemic changes.

Answer 15

Here's a version that outputs the same as the script by #loolotux, but is much faster(while less readable).
That loop takes about 10 secs on my machine, my version takes 0.019 s, which mattered to me because I wanted to make it into a cgi page.
join -t / -1 3 -2 3 \
<(grep VmSwap /proc/*/status |egrep -v '/proc/self|thread-self' | sort -k3,3 --field-separator=/ ) \
<(grep -H '' --binary-files=text /proc/*/cmdline |tr '\0' ' '|cut -c 1-200|egrep -v '/proc/self|/thread-self'|sort -k3,3 --field-separator=/ ) \
| cut -d/ -f1,4,7- \
| sed 's/status//; s/cmdline//' \
| sort -h -k3,3 --field-separator=:\
| tee >(awk -F: '{s+=$3} END {printf "\nTotal Swap Usage = %.0f kB\n",s}') /dev/null

Answer 16

I don't know of any direct answer as how to find exactly what process is using the swap space, however, this link may be helpful. Another good one is over here
Also, use a good tool like htop to see which processes are using a lot of memory and how much swap overall is being used.

Answer 17

iotop is a very useful tool. It gives live stats of I/O and swap usage per process/thread. By default it shows per thread but you can do iotop -P to get per process info. This is not available by default. You may have to install via rpm/apt.

Answer 18

You can use Procpath (author here), to simplify parsing of VmSwap from /proc/$PID/status.
$ procpath record -f stat,cmdline,status -r 1 -d db.sqlite
$ sqlite3 -column db.sqlite \
'SELECT status_name, status_vmswap FROM record ORDER BY status_vmswap DESC LIMIT 5'
Web Content 192136
okular 186872
thunderbird 183692
Web Content 143404
MainThread 86300
You can also plot VmSwap of processes of interest over time like this. Here I'm recording my Firefox process tree while opening a couple tens of tabs along with statrting a memory-hungry application to try to cause it to swap (which wasn't convincing for Firefox, but your kilometrage may vary).
$ procpath record -f stat,cmdline,status -i 1 -d db2.sqlite \
'$..children[?(#.stat.pid == 6029)]'
# interrupt by Ctrl+C
$ procpath plot -d db2.sqlite -q cpu --custom-value-expr status_vmswap \
--title "CPU usage, % vs Swap, kB"

Answer 19

The same answer as #lolotux, but with sorted output:
printf 'Computing swap usage...\n';
swap_usages="$(
SUM=0
OVERALL=0
for DIR in `find /proc/ -maxdepth 1 -type d -regex "^/proc/[0-9]+"`
do
PID="$(printf '%s' "$DIR" | cut -d / -f 3)"
PROGNAME=`ps -p $PID -o comm --no-headers`
for SWAP in `grep VmSwap $DIR/status 2>/dev/null | awk '{ print $2 }'`
do
let SUM=$SUM+$SWAP
done
if (( $SUM > 0 )); then
printf "$SUM KB ($PROGNAME) swapped PID=$PID\\n"
fi
let OVERALL=$OVERALL+$SUM
SUM=0
break
done
printf '9999999999 Overall swap used: %s KB\n' "$OVERALL"
)"
printf '%s' "$swap_usages" | sort -nk1
Example output:
Computing swap usage...
2064 KB (systemd) swapped PID=1
59620 KB (xfdesktop) swapped PID=21405
64484 KB (nemo) swapped PID=763627
66740 KB (teamviewerd) swapped PID=1618
68244 KB (flameshot) swapped PID=84209
763136 KB (plugin_host) swapped PID=1881345
1412480 KB (java) swapped PID=43402
3864548 KB (sublime_text) swapped PID=1881327
9999999999 Overall swap used: 2064 KB

Answer 20

I use this, useful if you only have /proc and nothing else useful. Just set nr to the number of top swappers you want to see and it will tell you the process name, swap footprint(MB) and it's full process line from ps -ef:
nr=10;for pid in $(for file in /proc//status ; do awk '/VmSwap|Name|^Pid/{printf $2 " " $3}END{ print ""}' $file; done | sort -k 3 -n -r|head -${nr}|awk '{ print $2 }');do awk '/VmSwap|Name|^Pid/{printf $2 " " $3}END{ print ""}' /proc/$pid/status|awk '{print $1" "$2" "$3/1024" MB"}'|sed -e 's/.[0-9]//g';ps -ef|awk "$2==$pid {print}";echo;done