Bash top - Display Linux Tasks

All examples below use a hypothetical output for demonstration:

top - 08:00:01 up 10 days,  3:22,  3 users,  load average: 0.01, 0.05, 0.10
Tasks: 123 total,   1 running, 122 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.7 us,  0.3 sy,  0.0 ni, 98.7 id,  0.3 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  8163100 total,  123456 free,  234567 used,  345678 buff/cache
KiB Swap:  2097148 total,  1048576 free,  1048572 used.  456789 avail Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 user      20   0  123456  12345   1234 S   0.3  0.2   0:01.23 bash
 5678 user      20   0  234567  23456   2345 S   0.5  0.3   0:02.34 python
 9101 user      20   0  345678  34567   3456 S   0.7  0.4   0:03.45 node

Understanding the Output

The top command output consists of several columns, each representing different aspects of the system's processes:

• PID: Process ID, a unique identifier for each process.
• USER: The user account that owns the process.
• PR: Priority of the process.
• NI: Nice value, which affects scheduling priority.
• VIRT: Virtual memory size used by the process.
• RES: Resident memory size, the non-swapped physical memory the process uses.
• SHR: Shared memory size.
• S: Process status (e.g., S for sleeping, R for running).
• %CPU: CPU usage percentage.
• %MEM: Memory usage percentage.
• TIME+: Total CPU time the process has used since it started.
• COMMAND: The command that started the process.

Basic Usage

To display Linux tasks, use top:

top
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 user      20   0  123456  12345   1234 S   0.3  0.2   0:01.23 bash
 5678 user      20   0  234567  23456   2345 S   0.5  0.3   0:02.34 python
 9101 user      20   0  345678  34567   3456 S   0.7  0.4   0:03.45 node

Options

The top command has options to change how it works:

• -d - Set the time between updates
• -p - Monitor specific PIDs
• -u - Show tasks for a specific user
• -n - Set the number of iterations
• -b - Batch mode operation

Set Update Interval

The -d option allows you to set the time between updates.

top -d 5
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 user      20   0  123456  12345   1234 S   0.3  0.2   0:01.23 bash

Monitor Specific PIDs

The -p option allows you to monitor specific PIDs.

top -p 1234
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 user      20   0  123456  12345   1234 S   0.3  0.2   0:01.23 bash

Show Tasks for a Specific User

The -u option allows you to show tasks for a specific user.

top -u user
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 user      20   0  123456  12345   1234 S   0.3  0.2   0:01.23 bash

Set Number of Iterations

The -n option allows you to set the number of iterations before top exits.

top -n 2
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 user      20   0  123456  12345   1234 S   0.3  0.2   0:01.23 bash

Batch Mode Operation

The -b option allows top to run in batch mode, suitable for sending output to other programs or files.

top -b -n 1
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 user      20   0  123456  12345   1234 S   0.3  0.2   0:01.23 bash

Combining Options

Options can be combined to provide more detailed output. For example, top -b -n 1 runs top in batch mode for one iteration.

top -b -n 1
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 user      20   0  123456  12345   1234 S   0.3  0.2   0:01.23 bash