Shell script to check top memory & cpu consuming process in Linux

Earlier I had written an article with the commands to check memory usage per process in Linux. Now what if you wish to check top cpu and memory utilization process, so in this article we will go one step ahead and write a shell script to check top CPU consuming process and top Memory consuming process in Linux

 

Tools to check top CPU consuming process

If you just wish to monitor top CPU consuming process then there are various utilities such as top, vmstat, sar which can help you check high cpu usage process and  give you runtime CPU utilization status in detail.

 

top - check high CPU utilization process

top is a very useful tool for system administrators to monitor system resources. To check top CPU consuming process execute top and then press "shift + p" which will sort and list the high CPU usage process in Linux. As you see here currently

top - 20:32:26 up  9:31,  3 users,  load average: 0.60, 0.17, 0.30
Tasks: 120 total,   3 running, 117 sleeping,   0 stopped,   0 zombie
%Cpu(s): 27.4 us, 33.6 sy,  0.0 ni, 23.4 id, 13.7 wa,  0.0 hi,  2.0 si,  0.0 st
KiB Mem :  3880016 total,  2932020 free,   399832 used,   548164 buff/cache
KiB Swap:  1048572 total,  1048572 free,        0 used.  3268824 avail Mem
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
13681 root      20   0    7312    100      0 R  99.7  0.0   0:06.42 stress
13683 root      20   0  269460 128468    124 R  99.3  3.3   0:06.41 stress
13684 root      20   0  108000    616    520 R  51.0  0.0   0:01.54 dd
  427 root       0 -20       0      0      0 S   2.0  0.0   0:00.81 kworker/0:1H

As you see currently stress and dd are our top CPU consuming process

 

sar- check CPU usage

sar is another powerful monitoring tool which is used by most professionals (my personal favourite). I have written another article with all the system resources you can monitor using sar.

To check CPU usage using sar you can use -u. For example to check CPU usage for two intervals with a gap of 1 second

# sar -u 1 2
Linux 3.10.0-1062.4.1.el7.x86_64 (server1.example.com)  01/10/2020      _x86_64_        (4 CPU)

08:45:20 PM     CPU     %user     %nice   %system   %iowait    %steal     %idle
08:45:21 PM     all     26.87      0.00     36.43     12.92      0.00     23.77
08:45:22 PM     all     27.46      0.00     35.49     13.99      0.00     23.06
Average:        all     27.17      0.00     35.96     13.45      0.00     23.42

Similarly you can use -P to check CPU usage per core. For example to check CPU usage per core for 2 interval with 1 second gap use below command. As you see CPU0 is most used while CPU 1-3 are mostly idle. You can also assign a service to a specific core or distribute CPU and other resources to services by creating cgroups

# sar -P ALL 1 2
Linux 3.10.0-1062.4.1.el7.x86_64 (server1.example.com)  01/10/2020      _x86_64_        (4 CPU)

08:54:56 PM     CPU     %user     %nice   %system   %iowait    %steal     %idle
08:54:57 PM     all     27.32      0.00     35.31     14.43      0.00     22.94
08:54:57 PM       0      0.00      0.00      7.37      0.00      0.00     92.63
08:54:57 PM       1      1.09      0.00     39.13     59.78      0.00      0.00
08:54:57 PM       2      5.05      0.00     94.95      0.00      0.00      0.00
08:54:57 PM       3    100.00      0.00      0.00      0.00      0.00      0.00

08:54:57 PM     CPU     %user     %nice   %system   %iowait    %steal     %idle
08:54:58 PM     all     26.99      0.00     36.76     13.62      0.00     22.62
08:54:58 PM       0      0.00      0.00      9.28      0.00      0.00     90.72
08:54:58 PM       1      0.00      0.00     42.39     57.61      0.00      0.00
08:54:58 PM       2      6.93      0.00     93.07      0.00      0.00      0.00
08:54:58 PM       3    100.00      0.00      0.00      0.00      0.00      0.00

Average:        CPU     %user     %nice   %system   %iowait    %steal     %idle
Average:        all     27.16      0.00     36.04     14.03      0.00     22.78
Average:          0      0.00      0.00      8.33      0.00      0.00     91.67
Average:          1      0.54      0.00     40.76     58.70      0.00      0.00
Average:          2      6.00      0.00     94.00      0.00      0.00      0.00
Average:          3    100.00      0.00      0.00      0.00      0.00      0.00

To check CPU usage per CPU core you can use sar -P <CPU Core> for example to check CPU0 use sar -P 0

 

Tools to check top Memory consuming process

Similar to the above chapter, same tools can also be used to monitor top memory consuming process. I will give some examples using top and sar commands

 

top - check high memory utilization process

You can execute top without any arguments on the terminal and then press "shift + m" to sort and print current high memory utilization process in Linux.

top - 21:05:23 up 10:04,  3 users,  load average: 3.13, 3.05, 2.73
Tasks: 121 total,   5 running, 116 sleeping,   0 stopped,   0 zombie
%Cpu(s): 27.5 us, 34.1 sy,  0.0 ni, 22.8 id, 14.0 wa,  0.0 hi,  1.6 si,  0.0 st
KiB Mem :  3880016 total,  2457248 free,   178352 used,  1244416 buff/cache
KiB Swap:  1048572 total,  1048572 free,        0 used.  3462736 avail Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
13683 root      20   0  269460  54740    124 R 100.0  1.4  30:47.68 stress
  857 root      20   0  358748  29472   7048 S   0.0  0.8   0:00.63 firewalld
 1193 root      20   0  574200  17512   6136 S   0.0  0.5   0:05.59 tuned
  841 polkitd   20   0  613016  12952   4892 S   0.0  0.3   0:00.07 polkitd

Here currently as you see the memory usage is not very high and only few process are consuming memory where stress is the leading scorer.

 

sar - check memory usage

with sar use -r to check memory usage in Linux. For example here I will print memory usage for 2 intervals with 1 second gap.

# sar -r 1 2
Linux 3.10.0-1062.4.1.el7.x86_64 (server1.example.com)  01/10/2020      _x86_64_        (4 CPU)

09:11:20 PM kbmemfree kbmemused  %memused kbbuffers  kbcached  kbcommit   %commit  kbactive   kbinact   kbdirty
09:11:21 PM   2274656   1605360     41.38     39156   1150276    552848     11.22   1202516    234216         0
09:11:22 PM   2337276   1542740     39.76     39156   1150276    552848     11.22   1155908    234216         0
Average:      2305966   1574050     40.57     39156   1150276    552848     11.22   1179212    234216         0

 

There are many other tools such as vmstat, collectl, nmon etc. But since our main intention of this article is to check top CPU and memory consuming process using shell script, we will jump to our sample shell script.

 

Command to check top CPU consuming process

We will use ps to check top CPU consuming process in Linux.

# ps -eocomm,pcpu | egrep -v '(0.0)|(%CPU)'
kworker/0:1H     0.3
stress          99.9
stress          46.7
stress          99.9
kworker/u8:2     0.3
kworker/u8:1     0.3

We can utilise this command in a shell script to check top CPU consuming process.

Command to check top Memory consuming process

Here also we will use ps command to check top memory consuming process with a little change compared to above command

# ps -eocomm,pmem | egrep -v '(0.0)|(%MEM)'
systemd          0.1
polkitd          0.1
NetworkManager   0.1
tuned            0.2
java            82.1
metricbeat       1.4
rsyslogd         0.1
iscsid           0.2

Here,

• The -e option specifies to collect data on all processes, not just this session's tasks.
• The -o option specifies an output format.
• The comm, pcpu and pmem words specify reporting the command name, percentage of CPU and percentage of memory respectively.
• This ps command generates a line with the command name and current percentage of CPU and memory usage for each running process.
• These lines are filtered with grep to remove lines where there was no CPU usage (%CPU is 0.0) with the COMMAND %CPU header and no MEM usage (%MEM is 0.0) with the COMMAND %MEM header.

 

Shell script to check top CPU consuming process for an hour

Now we can utilise this command in a shell script to get top memory and cpu consuming process in Linux. The below sample script collects and prints top cpu consuming process for an hour.
I have added a trap for Ctrl + C so that if end user does not wish to wait for an hour and wants to check high cpu utilization process then he can press Ctrl + C to send an interrupt.

#!/bin/bash
# Name: monitor_cpu_usage.sh
# Description: Script to check top cpu consuming process for 1 hour

# Change the SECS to total seconds to monitor CPU usage.
# UNIT_TIME is the interval in seconds between each sampling


function report_utilisation {
  # Process collected data
  echo
  echo "CPU eaters :"

  cat /tmp/cpu_usage.$$ | 
awk '
{ process[$1]+=$2; }
END{
  for(i in process)
  {
    printf("%-20s %s\n",i, process[i]) ;
  }

   }' | sort -nrk 2 | head

# Remove the temporary log file
rm /tmp/cpu_usage.$$
exit 0
}

trap 'report_utilisation' INT

SECS=3600
UNIT_TIME=10

STEPS=$(( $SECS / $UNIT_TIME ))

echo "Watching CPU usage... ;"

# Collect data in temp file
for((i=0;i<$STEPS;i++)); do
    ps -eocomm,pcpu | egrep -v '(0.0)|(%CPU)' >> /tmp/cpu_usage.$$
    sleep $UNIT_TIME
done

report_utilisation

Provide executable permission to the script

# chmod u+x /tmp/monitor_cpu_usage.sh

Now execute the script. This gives us a cumulative value of the overall CPU usage for the time the script was running

# /tmp/monitor_cpu_usage.sh
Watching CPU usage...
^C
CPU eaters :
stress               235.1
java                 15.7
metricbeat           3.1
sshd                 0.4
systemd-journal      0.1
systemd              0.1
rcu_sched            0.1
kworker/u8:0         0.1
kworker/0:1H         0.1

 

Shell script to check top Memory consuming process for an hour

We can use the same script by modifying certain variables and commands to check top memory consuming process:

#!/bin/bash
# Name: monitor_mem_usage.sh
# Description: Script to check top memory consuming process for 1 hour

# Change the SECS to total seconds to monitor Memory usage.
# UNIT_TIME is the interval in seconds between each sampling


function report_utilisation {
  # Process collected data
  echo
  echo "Memory eaters :"

  cat /tmp/mem_usage.$$ | 
awk '
{ process[$1]+=$2; }
END{
  for(i in process)
  {
    printf("%-20s %s\n",i, process[i]) ;
  }

   }' | sort -nrk 2 | head

# Remove the temporary log file
rm /tmp/mem_usage.$$
exit 0
}

trap 'report_utilisation' INT

SECS=3600
UNIT_TIME=10

STEPS=$(( $SECS / $UNIT_TIME ))

echo "Watching Memory usage... ;"

# Collect data in temp file
for((i=0;i<$STEPS;i++)); do 
    ps -eocomm,pmem | egrep -v '(0.0)|(%MEM)' >> /tmp/mem_usage.$$
    sleep $UNIT_TIME
done

report_utilisation

Provide executable permission to the script

# chmod u+x /tmp/monitor_mem_usage.sh

Now we will run the script for few minutes and then press ctrl + C to send an interrupt

# /tmp/monitor_mem_usage.sh
Watching Memory usage...
^C
Memory eaters :
java                 82.1
stress               1.6
metricbeat           1.5
tuned                0.2
iscsid               0.2
systemd              0.1
rsyslogd             0.1
polkitd              0.1
NetworkManager       0.1

 

How this script works?

• Based on UNIT_TIME variable, the ps -eocomm,pcpu or ps -eocomm,pmem command generates a report on the system activity at that time and stores in the temporary file
• The temporary file is named /tmp/cpu_usage.$$. Here, $$ is a script variable that holds the process ID (PID) of the current script. For example, if the script's PID is 1345, the temporary file will be named /tmp/cpu_usage.1345
• The statistics file will be ready after one hour and will contain 60 sets of entries, corresponding to the system status at each minute.
• The awk script sums the total CPU and memory usage for each process into an associative array named process. This array uses the process name as array index.
• Finally, awk sorts the result with a numeric reverse sort according to the total CPU and Memory usage and uses head to limit the report to the top 10 usage entries.

 

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