Using the top Command
The top command is used to display Linux tasks.
It's a powerful tool for monitoring system performance in real-time.
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 nodeUnderstanding 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 :
Example: Basic Usage
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 nodeOptions
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.
Example: Set Update Interval
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 bashMonitor Specific PIDs
The -p option allows you to monitor specific PIDs.
Example: 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 bashShow Tasks for a Specific User
The -u option allows you to show tasks for a specific user.
Example: 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 bashSet Number of Iterations
The -n option allows you to set the number of iterations before top exits.
Example: Set Number of Iterations
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 bashBatch Mode Operation
The -b option allows top to run in batch mode, suitable for sending output to other programs or files.
Example: Batch Mode Operation
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 bashCombining Options
Options can be combined to provide more detailed output. For example, top -b -n 1 runs top in batch mode for one iteration.
Example: Combine Options
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