Checking CPU usage in Linux shows whether slow commands, high load, or alert noise is tied to processor time. When a server feels laggy, top separates active CPU work from idle capacity and I/O wait before the investigation moves to storage, memory, or network paths.

The top display combines a system summary with a process table. The %Cpu(s) row shows user time, system time, idle time, I/O wait, interrupt time, and stolen virtual CPU time, while the %CPU column shows each task's processor share since the last refresh.

Use the live view for short observations and top -b -n 1 for a copyable snapshot in tickets, chat, or incident notes. A single busy thread often appears near 100.0 in the %CPU column even when the system still has idle capacity, and multithreaded tasks can exceed 100 on multi-CPU systems. In containers, load averages may reflect the host while the task table only shows processes visible inside the container namespace.

Related: How to check load average in Linux
Related: How to check process CPU and memory usage in Linux

Steps to show CPU usage in Linux with top:

  1. Start top to open the live CPU summary and process table. 
    $ top

    The summary area starts with load average, task counts, and the combined %Cpu(s) line.

  2. Read the %Cpu(s) line near the top of the screen. 
    %Cpu(s):  3.4 us,  9.1 sy,  0.0 ni, 86.4 id,  1.1 wa,  0.0 hi,  0.0 si,  0.0 st

    us and sy show active CPU work, id shows idle capacity, and wa shows time waiting for I/O completion.

  3. Press 1 when a single thread may be saturating one CPU.

    1 switches the combined summary into separate %Cpu0, %Cpu1, and later CPU lines when the terminal has enough room.

  4. Press P when the busiest tasks are not at the top.

    P sorts the task table by the %CPU column.

  5. Capture a one-shot CPU snapshot for a ticket or incident note. 
    $ top -b -n 1
top - 02:39:04 up 21:02,  0 users,  load average: 0.26, 0.48, 0.52
Tasks:   3 total,   2 running,   1 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.4 us,  9.1 sy,  0.0 ni, 86.4 id,  1.1 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  11948.5 total,   7681.1 free,    938.4 used,   3576.2 buff/cache
MiB Swap:   4096.0 total,   4096.0 free,      0.0 used.  11010.1 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
     39 root      20   0   16668   5724   4584 R 100.0   0.0   0:01.21 yes
      1 root      20   0    5872   3212   2952 S   0.0   0.0   0:00.00 bash
     41 root      20   0    8312   4276   2376 R   0.0   0.0   0:00.00 top

    The %Cpu(s) line shows the system-wide split, while the %CPU column identifies the process using that time.

  6. Press q to leave top when the check is complete.