How to Save Top Command Output to a File

To Save Top Command Output to a File

Linux top command is highly used by system administrators to display system statistics in real time regarding system uptime and load average, used memory, running tasks, a summary of processes or threads and detailed information about each running process.

Saving Top Command Output

First, we will redirect the output of top command to top.txt file in the current working directory by running the following command.

root@linuxhelp:~# top -b -n 1 >  top.txt

And then, read the resulted file, use a command line file reader utility, such as cat command, less or more as follows.

root@linuxhelp:~# less top.txt
top - 05:27:38 up  1:09,  1 user,  load average: 0.36, 0.12, 0.11
Tasks: 228 total,   1 running, 227 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.7 us,  1.9 sy,  1.2 ni, 91.8 id,  1.3 wa,  0.0 hi,  0.1 si,  0.0 st
KiB Mem :  2029876 total,   331784 free,   743740 used,   954352 buff/cache
KiB Swap:  2094076 total,  2091308 free,     2768 used.  1074884 avail Mem 

   PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
  7801 root      20   0   41800   3832   3224 R  5.9  0.2   0:00.02 top
     1 root      20   0  119744   5944   4040 S  0.0  0.3   0:02.69 systemd
.
.

After that, you need to grab five iteration of top command, execute the command as shown below.

root@linuxhelp:~# top -b -n 5 >  top-5iterations.txt

In order to display only the number of running tasks from the resulted file, use the grep filter, as shown in the below command example.

root@linuxhelp:~# cat top-5iterations.txt | grep Tasks
Tasks: 226 total,   1 running, 225 sleeping,   0 stopped,   0 zombie
Tasks: 226 total,   2 running, 224 sleeping,   0 stopped,   0 zombie
Tasks: 226 total,   1 running, 225 sleeping,   0 stopped,   0 zombie
Tasks: 226 total,   2 running, 224 sleeping,   0 stopped,   0 zombie
Tasks: 226 total,   1 running, 225 sleeping,   0 stopped,   0 zombie

To take a snapshot of a specific process in top utility, execute command with the PID (-p) flag. To get the PID of a running process, issue pidof command against the name of the running process.  In this example we’ ll monitor the cron process via top command by taking three snapshots of the PID.

root@linuxhelp:~# pidof crond
root@linuxhelp:~# top -p 678 -b -n3 >  cron.txt
root@linuxhelp:~# cat cron.txt
top - 05:33:52 up  1:13,  1 user,  load average: 0.60, 0.20, 0.13
Tasks:   0 total,   0 running,   0 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.6 us,  1.8 sy,  1.1 ni, 92.2 id,  1.2 wa,  0.0 hi,  0.1 si,  0.0 st
KiB Mem :  2029876 total,   328304 free,   747112 used,   954460 buff/cache
KiB Swap:  2094076 total,  2091308 free,     2768 used.  1071512 avail Mem

Using for iteration loop, we can display a process statistics via its PID, each two seconds, as shown in the below example. The output of the loop can also be redirected to a file. 

root@linuxhelp:~# for i in {1..4}  do sleep 2 & &  top -b -p 678 -n1 | tail -1   done 
   PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
   PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
   PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
   PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND

Now, you shall redirect loop output to file.

root@linuxhelp:~# for i in {1..4}  do sleep 2 & &  top -b -p 678 -n1 | tail -1   done > >  cron.txt
root@linuxhelp:~# cat cron.txt
top - 05:33:52 up  1:13,  1 user,  load average: 0.60, 0.20, 0.13
Tasks:   0 total,   0 running,   0 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.6 us,  1.8 sy,  1.1 ni, 92.2 id,  1.2 wa,  0.0 hi,  0.1 si,  0.0 st
KiB Mem :  2029876 total,   328304 free,   747112 used,   954460 buff/cache
KiB Swap:  2094076 total,  2091308 free,     2768 used.  1071512 avail Mem

These are just a few examples on how you can monitor and gather system and process statistics via top command.