/proc/stat kernel/system statistics. Varies with architecture. Common entries include:
cpu 10132153 290696 3084719 46828483 16683 0 25195 0 175628 0 cpu0 1393280 32966 572056 13343292 6130 0 17875 0 23933 0 The amount of time, measured in units of USER_HZ (1/100ths of a second on most architectures, use sysconf(_SC_CLK_TCK) to obtain the right value), that the system ("cpu" line) or the specific CPU ("cpuN" line) spent in various states:
user (1) Time spent in user mode.
nice (2) Time spent in user mode with low priority (nice).
system (3) Time spent in system mode.
idle (4) Time spent in the idle task. This value should be USER_HZ times the second entry in the /proc/uptime pseudo-file.
iowait (since Linux 2.5.41) (5) Time waiting for I/O to complete. This value is not reliable, for the following reasons:
1. The CPU will not wait for I/O to complete; iowait is the time that a task is waiting for I/O to complete. When a CPU goes into idle state for outstanding task I/O, another task will be scheduled on this CPU.
2. On a multi-core CPU, the task waiting for I/O to complete is not running on any CPU, so the iowait of each CPU is difficult to calculate.
3. The value in this field may decrease in certain conditions.
irq (since Linux 2.6.0) (6) Time servicing interrupts.
softirq (since Linux 2.6.0) (7) Time servicing softirqs.
steal (since Linux 2.6.11) (8) Stolen time, which is the time spent in other operating systems when running in a virtualized environment
guest (since Linux 2.6.24) (9) Time spent running a virtual CPU for guest operating systems under the control of the Linux kernel.
guest_nice (since Linux 2.6.33) (10) Time spent running a niced guest (virtual CPU for guest operating systems under the control of the Linux kernel).
We cat /proc/stat and store the content as stat1, sleep a while, cat-store again as stat2.
$ man5 proc /proc/[pid]/stat Status information about the process. This is used by ps(1). It is defined in the kernel source file fs/proc/array.c.
The fields, in order, with their proper scanf(3) format specifiers, are listed below. Whether or not certain of these fields display valid information is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS | PTRACE_MODE_NOAUDIT check (refer to ptrace(2)). If the check denies access, then the field value is displayed as 0. The affected fields are indicated with the marking [PT].
(1) pid %d The process ID.
(2) comm %s The filename of the executable, in parentheses. Strings longer than TASK_COMM_LEN (16) characters (including the terminating null byte) are silently truncated. This is visible whether or not the executable is swapped out.
(3) state %c One of the following characters, indicating process state:
R Running
S Sleeping in an interruptible wait
D Waiting in uninterruptible disk sleep
Z Zombie
T Stopped (on a signal) or (before Linux 2.6.33) trace stopped
t Tracing stop (Linux 2.6.33 onward)
W Paging (only before Linux 2.6.0)
X Dead (from Linux 2.6.0 onward)
x Dead (Linux 2.6.33 to 3.13 only)
K Wakekill (Linux 2.6.33 to 3.13 only)
W Waking (Linux 2.6.33 to 3.13 only)
P Parked (Linux 3.9 to 3.13 only)
(4) ppid %d The PID of the parent of this process.
(5) pgrp %d The process group ID of the process.
(6) session %d The session ID of the process.
(7) tty_nr %d The controlling terminal of the process. (The minor device number is contained in the combination of bits 31 to 20 and 7 to 0; the major device number is in bits 15 to 8.)
(8) tpgid %d The ID of the foreground process group of the controlling terminal of the process.
(9) flags %u The kernel flags word of the process. For bit meanings, see the PF_* defines in the Linux kernel source file include/linux/sched.h. Details depend on the kernel version.
The format for this field was %lu before Linux 2.6.
(10) minflt %lu The number of minor faults the process has made which have not required loading a memory page from disk.
(11) cminflt %lu The number of minor faults that the process's waited-for children have made.
(12) majflt %lu The number of major faults the process has made which have required loading a memory page from disk.
(13) cmajflt %lu The number of major faults that the process's waited-for children have made.
(14) utime %lu Amount of time that this process has been scheduled in user mode, measured in clock ticks (divide by sysconf(_SC_CLK_TCK)). This includes guest time, guest_time (time spent running a virtual CPU, see below), so that applications that are not aware of the guest time field do not lose that time from their calculations.
(15) stime %lu Amount of time that this process has been scheduled in kernel mode, measured in clock ticks (divide by sysconf(_SC_CLK_TCK)).
(16) cutime %ld Amount of time that this process's waited-for children have been scheduled in user mode, measured in clock ticks (divide by sysconf(_SC_CLK_TCK)). (See also times(2).) This includes guest time, cguest_time (time spent running a virtual CPU, see below).
(17) cstime %ld Amount of time that this process's waited-for children have been scheduled in kernel mode, measured in clock ticks (divide by sysconf(_SC_CLK_TCK)).
(18) priority %ld (Explanation for Linux 2.6) For processes running a real-time scheduling policy (policy below; see sched_setscheduler(2)), this is the negated scheduling priority, minus one; that is, a number in the range -2 to -100, corresponding to real-time priorities 1 to 99. For processes running under a non-real-time scheduling policy, this is the raw nice value (setpriority(2)) as represented in the kernel. The kernel stores nice values as numbers in the range 0 (high) to 39 (low), corresponding to the user-visible nice range of -20 to 19.
Before Linux 2.6, this was a scaled value based on the scheduler weighting given to this process.
(19) nice %ld The nice value (see setpriority(2)), a value in the range 19 (low priority) to -20 (high priority).
(20) num_threads %ld Number of threads in this process (since Linux 2.6). Before kernel 2.6, this field was hard coded to 0 as a placeholder for an earlier removed field.
(21) itrealvalue %ld The time in jiffies before the next SIGALRM is sent to the process due to an interval timer. Since kernel 2.6.17, this field is no longer maintained, and is hard coded as 0.
(22) starttime %llu The time the process started after system boot. In kernels before Linux 2.6, this value was expressed in jiffies. Since Linux 2.6, the value is expressed in clock ticks (divide by sysconf(_SC_CLK_TCK)).
The format for this field was %lu before Linux 2.6.
(23) vsize %lu Virtual memory size in bytes.
(24) rss %ld Resident Set Size: number of pages the process has in real memory. This is just the pages which count toward text, data, or stack space. This does not include pages which have not been demand-loaded in, or which are swapped out. This value is inaccurate; see /proc/[pid]/statm below.
(25) rsslim %lu Current soft limit in bytes on the rss of the process; see the description of RLIMIT_RSS in getrlimit(2).
(26) startcode %lu [PT] The address above which program text can run.
(27) endcode %lu [PT] The address below which program text can run.
(28) startstack %lu [PT] The address of the start (i.e., bottom) of the stack.
(29) kstkesp %lu [PT] The current value of ESP (stack pointer), as found in the kernel stack page for the process.
(30) kstkeip %lu [PT] The current EIP (instruction pointer).
(31) signal %lu The bitmap of pending signals, displayed as a decimal number. Obsolete, because it does not provide information on real-time signals; use /proc/[pid]/status instead.
(32) blocked %lu The bitmap of blocked signals, displayed as a decimal number. Obsolete, because it does not provide information on real-time signals; use /proc/[pid]/status instead.
(33) sigignore %lu The bitmap of ignored signals, displayed as a decimal number. Obsolete, because it does not provide information on real-time signals; use /proc/[pid]/status instead.
(34) sigcatch %lu The bitmap of caught signals, displayed as a decimal number. Obsolete, because it does not provide information on real-time signals; use /proc/[pid]/status instead.
(35) wchan %lu [PT] This is the "channel" in which the process is waiting. It is the address of a location in the kernel where the process is sleeping. The corresponding symbolic name can be found in /proc/[pid]/wchan.
(36) nswap %lu Number of pages swapped (not maintained).
(37) cnswap %lu Cumulative nswap for child processes (not maintained).
(38) exit_signal %d (since Linux 2.1.22) Signal to be sent to parent when we die.
(39) processor %d (since Linux 2.2.8) CPU number last executed on.
(40) rt_priority %u (since Linux 2.5.19) Real-time scheduling priority, a number in the range 1 to 99 for processes scheduled under a real- time policy, or 0, for non-real-time processes (see sched_setscheduler(2)).
(41) policy %u (since Linux 2.5.19) Scheduling policy (see sched_setscheduler(2)). Decode using the SCHED_* constants in linux/sched.h.
The format for this field was %lu before Linux 2.6.22.
(42) delayacct_blkio_ticks %llu (since Linux 2.6.18) Aggregated block I/O delays, measured in clock ticks (centiseconds).
(43) guest_time %lu (since Linux 2.6.24) Guest time of the process (time spent running a virtual CPU for a guest operating system), measured in clock ticks (divide by sysconf(_SC_CLK_TCK)).
(44) cguest_time %ld (since Linux 2.6.24) Guest time of the process's children, measured in clock ticks (divide by sysconf(_SC_CLK_TCK)).
(45) start_data %lu (since Linux 3.3) [PT] Address above which program initialized and uninitialized (BSS) data are placed.
(46) end_data %lu (since Linux 3.3) [PT] Address below which program initialized and uninitialized (BSS) data are placed.
(47) start_brk %lu (since Linux 3.3) [PT] Address above which program heap can be expanded with brk(2).
(48) arg_start %lu (since Linux 3.5) [PT] Address above which program command-line arguments (argv) are placed.
(49) arg_end %lu (since Linux 3.5) [PT] Address below program command-line arguments (argv) are placed.
(50) env_start %lu (since Linux 3.5) [PT] Address above which program environment is placed.
(51) env_end %lu (since Linux 3.5) [PT] Address below which program environment is placed.
(52) exit_code %d (since Linux 3.5) [PT] The thread's exit status in the form reported by waitpid(2).
So the cpu usage of one task is the cpu time used by the task(14 utime + 15 stime, unit is clock ticks) / the real time past (from /proc/uptime, unit is seconds).
We cat /proc/<pid>/stat and /proc/uptime, store the content as stat1 and uptime1, sleep a while, cat-store again as stat2 and uptime2.
1 2 3 4
cpu usage of task = ((stat2.utime+stat2.stime-stat1.utime-stat1.stime)/sysconf(_SC_CLK_TCK)) / (uptime2 - uptime1) * 100%
Usage is between 0 and (count of cpus) * 100%. If the task has multi thread and all run in different core together, than the cpu usage of task is larger than 100%. That`s different from the cpu usage of host.
![](http://www.tumblr.com/share/link?url=https://www.liaol.net/2022/05/how-to-calculate-the-cpu-usage-in-linux/&name=how-to-calculate-the-cpu-usage-in-linux&description=<p>As we know, one can use top or other tools to get cpu usage。 Below is the output of top</p>
<p><img src="https://tvax1.sinaimg.cn/large/e6c9d24ely1h2qttn2s9wj21jk0rc45x.jpg" alt></p>
<p>Now I will explain how to calculate the CPU usage in Linux.</p>){kind=link}
