It is important to find the process or application hogging memory of the system in case of a performance issue. The post lists few of the basic commands to calculate memory usage on a general Linux system.
1. Calculate memory usage using SAR
# sar -r 1 10 Linux 2.6.32-504.el6.x86_64 (geeklab) 03/05/2018 _x86_64_ (16 CPU) 10:17:41 AM kbmemfree kbmemused %memused kbbuffers kbcached kbcommit %commit 10:17:42 AM 1772488 31104712 94.61 382184 23831756 11675188 11.86 10:17:43 AM 1777348 31099852 94.59 382184 23831756 11675188 11.86 10:17:44 AM 1778412 31098788 94.59 382184 23831756 11675188 11.86 10:17:45 AM 1776720 31100480 94.60 382184 23831756 11675072 11.86 10:17:46 AM 1777932 31099268 94.59 382184 23831760 11675072 11.86 10:17:47 AM 1780848 31096352 94.58 382184 23831760 11675072 11.86 10:17:48 AM 1774460 31102740 94.60 382184 23831760 11675644 11.86 10:17:49 AM 1740080 31137120 94.71 382184 23831760 11717568 11.91 10:17:50 AM 1773608 31103592 94.61 382184 23831708 11675076 11.86 10:17:51 AM 1774752 31102448 94.60 382184 23831796 11675076 11.86 Average: 1772665 31104535 94.61 382184 23831757 11679414 11.87
To calculate free memory from Average value use the below formula:
kbmemfree + kbbuffers + kbcached = actual free memory on the system
Using above example:
1772665 + 382184 + 23831757 = 25986606KB
That’s around 24.78GB free memory.
2. Calculate memory usage using free command
# free -m
total used free shared buffers cached
Mem: 32106 30382 1723 3031 373 23273
-/+ buffers/cache: 6736 25370
Swap: 63999 2 63997 From above example, to get free memory on the system use:
-/+ buffers/cache ==> free column
Free column reports 25370 MB so that match sar output calculation as well ( keeping in mind that in SAR Average value was used )
To get used memory on system use:
-/+ buffers/cache ==> used column
In our case the used memory is 6736MB.
3. Find Top 10 users are which are consuming more memory on system in percentage
Please use simple shell syntax which utilize ps command:
# ps -eo user,pcpu,pmem | tail -n +2 | awk '{num[$1]++; cpu[$1] += $2; mem[$1] += $3} END{printf("NPROC\tUSER\tCPU\tMEM\n"); for (user in cpu) printf("%d\t%s\t%.2f\t%.2f\n",num[user], user, cpu[user], mem[user]) }'
NPROC USER CPU MEM
29 oracle 0.10 4.00
1 ntp 0.00 0.00
1 rpc 0.00 0.00
5 user 0.00 0.00
1 dbus 0.00 0.00
1 mysql 0.00 0.30
12 daemon 0.00 0.60
2 postfix 0.00 0.00
12 apache1 2.40 4.80
1 rpcuser 0.00 0.00
349 root 7.70 3.30 From the above example observation, root has 349 processes which are taking 3.3% of memory, user oracle has 29 processes which are taking 4% of memory, user apache1 has 12 processes consuming around 4.8% of memory, that in total around 12%. Around 12% value can be also seen on sar ‘commit’ column.
4. Check 10 Top processes which are consuming RSS ( Resident Set Size )
Please use simple shell syntax which utilize ps command:
# ps -e -orss,pid=,user=,args=, | sort -b -k1,1n | pr -TW$COLUMNS| tail -10 74336 5509 root /opt/perf/bin/perfalarm 77212 8389 oracle /grid/CRS/bin/ohasd.bin reboot 78216 9731 root /opt/OV/lbin/agtrep/agtrep -start 96768 9808 root /opt/OV/hpcs/hpsensor 108580 12073 root /usr/lib/systemd/systemd-journald 136260 76477 root storapid start -name storapid 178316 5350 root /opt/OV/bin/oacore oacore /var/opt/OV/conf/oa/PipeDefinitions/oacore.xml 186168 10367 oracle /grid/CRS/bin/oraagent.bin 1013484 31562 root vxconfigd -x syslog 1317360 76463 root vxencryptd
First column is RSS, second one is PID, the third one is USER and fourth is Command Executed.
RSS value is the most important one here as this shows how much memory the process has actually allocated in KB, please do not use VSZ value which calculates ‘requested’ memory by process, as each process is allocating ‘overhead’ which is presented by VSZ value, where RSS reports true memory allocation by process.
After RSS output calculation, the ‘used‘ memory can be obtained and compared with -/+ buffers/cache – used column from the output of free command — both RSS and the output from the free command should match.