Process identifier (PID) is a number used by Linux / Unix kernels (and Windows operating systems) to identify a process. Usually, new processes are created using the fork() system call. Each PID (or so called tasks) can be monitored under Linux. In this quick tutorial, I will explain how to use the pidstat command for monitoring individual tasks currently being managed by the Linux kernel.
The pidstat command can also be used for monitoring the child processes of selected tasks and it can answer the following questions for you:
See stats for a particular process.See
disk stats for a particular process (e.g., disk I/O info for Apache/Nginx/Lighttpd and all of it's child processes).See statistics for threads associated with selected tasks.See
reports of CPU statistics for every active task.Find out: how many context switches a process makes?Find out: page faults and memory utilization for a particular process?Confirm memory leaks for a particular process.And much more.
The syntax is:
pidstatpidstat options interval count
Type the following command:
# pidstat
Sample outputs:
05:14:33 PM PID %usr %system %guest %CPU CPU Command05:14:33 PM 1 0.00 0.00 0.00 0.00 2 init05:14:33 PM 3 0.00 0.00 0.00 0.00 0 migration/005:14:33 PM 4 0.00 12.98 0.00 12.98 0 ksoftirqd/005:14:33 PM 5 0.00 0.00 0.00 0.00 0 migration/005:14:33 PM 6 0.00 0.00 0.00 0.00 0 watchdog/005:14:33 PM 7 0.00 0.00 0.00 0.00 1 migration/105:14:33 PM 8 0.00 0.00 0.00 0.00 1 migration/105:14:33 PM 9 0.00 5.70 0.00 5.70 1 ksoftirqd/105:14:33 PM 10 0.00 0.00 0.00 0.00 1 watchdog/1........05:14:33 PM 7915 0.00 0.00 0.00 0.00 1 nfsd405:14:33 PM 7917 0.00 0.01 0.00 0.01 6 nfsd05:14:33 PM 7918 0.00 0.01 0.00 0.01 6 nfsd05:14:33 PM 7919 0.00 0.01 0.00 0.01 6 nfsd05:14:33 PM 7920 0.00 0.02 0.00 0.02 1 nfsd05:14:33 PM 7921 0.00 0.01 0.00 0.01 4 nfsd05:14:33 PM 7922 0.00 0.01 0.00 0.01 6 nfsd05:14:33 PM 7923 0.00 0.02 0.00 0.02 4 nfsd05:14:33 PM 7924 0.00 0.01 0.00 0.01 5 nfsd05:14:33 PM 9254 0.00 0.00 0.00 0.00 6 php-cgi05:14:33 PM 9255 0.00 0.00 0.00 0.00 4 php-cgi05:14:33 PM 9266 0.00 0.00 0.00 0.00 4 php-cgi05:14:33 PM 12767 0.00 0.00 0.00 0.00 6 php-cgi05:14:33 PM 12776 0.00 0.00 0.00 0.00 6 php-cgi05:14:33 PM 12784 0.00 0.00 0.00 0.00 6 php-cgi05:14:33 PM 14800 0.00 0.00 0.00 0.00 6 php-cgi05:14:33 PM 14832 0.00 0.00 0.00 0.00 6 php-cgi05:14:33 PM 14836 0.00 0.00 0.00 0.00 4 php-cgi05:14:33 PM 14837 0.00 0.00 0.00 0.00 6 php-cgi05:14:33 PM 15016 0.00 0.00 0.00 0.00 6 sshd05:14:33 PM 15019 0.00 0.00 0.00 0.00 0 bash05:14:33 PM 15089 0.00 0.00 0.00 0.00 4 php-cgi05:14:33 PM 15090 0.00 0.00 0.00 0.00 4 php-cgi05:14:33 PM 15091 0.00 0.00 0.00 0.00 6 php-cgi
To see I/O statistics (kernels 2.6.20 and later only) for nfsd4 process run by PID # 13212, enter:
# pidstat -d -p 13212
# pidstat -d -p 13212 2 10
# pidstat -d -p 7114 1 50
Sample outputs (from mysqld server w/ PID # 7114):
Linux 2.6.32-279.el6.x86_64 (server1.cyberciti.biz) 08/21/2012 _x86_64_(8 CPU) 05:24:35 PM PID kB_rd/s kB_wr/s kB_ccwr/s Command05:24:36 PM 7114 0.00 40.00 0.00 mysqld05:24:37 PM 7114 0.00 64.00 64.00 mysqld05:24:38 PM 7114 0.00 44.00 8.00 mysqld05:24:39 PM 7114 0.00 24.00 0.00 mysqld05:24:40 PM 7114 0.00 128.00 128.00 mysqld05:24:41 PM 7114 0.00 88.00 64.00 mysqld05:24:42 PM 7114 0.00 92.00 0.00 mysqld05:24:43 PM 7114 0.00 152.00 64.00 mysqld05:24:44 PM 7114 0.00 48.00 0.00 mysqld05:24:45 PM 7114 0.00 44.00 0.00 mysqld05:24:46 PM 7114 8.00 1140.00 32.00 mysqld05:24:47 PM 7114 8.00 20124.00 3192.00 mysqld05:24:48 PM 7114 0.00 1992.00 2956.00 mysqld
You will see the following values:
PID - The identification number of the task being monitored.
kB_rd/s - Number of kilobytes the task has caused to be read from disk per second.
kB_wr/s - Number of kilobytes the task has caused, or shall cause to be written to disk per second.
kB_ccwr/s - Number of kilobytes whose writing to disk has been cancelled by the task. This may occur when the task truncates some irty pagecache. In this case, some IO which another task has been accounted for will not be happening.
Command - The command name of the task.
The following command will show you five reports of page faults statistics at two second intervals for the child processes of all tasks in the system:
# pidstat -T CHILD -r 2 5
Sample outputs:
Linux 2.6.32-279.el6.x86_64 (server1.cyberciti.biz) 08/21/2012 _x86_64_(8 CPU) 05:27:12 PM PID minflt-nr majflt-nr Command05:27:14 PM 1853 10 0 irqbalance05:27:14 PM 7114 3 0 mysqld05:27:14 PM 7910 2 0 rpc.idmapd05:27:14 PM 15089 1 0 php-cgi05:27:14 PM 15090 1 0 php-cgi05:27:14 PM 15091 2 0 php-cgi05:27:14 PM 15361 1 0 php-cgi05:27:14 PM 15362 1 0 php-cgi05:27:14 PM 15395 704 0 pidstat 05:27:14 PM PID minflt-nr majflt-nr Command05:27:16 PM 7114 169 0 mysqld05:27:16 PM 15359 1 0 php-cgi05:27:16 PM 15360 21 0 php-cgi05:27:16 PM 15361 2 0 php-cgi05:27:16 PM 15395 705 0 pidstat 05:27:16 PM PID minflt-nr majflt-nr Command05:27:18 PM 7114 14 0 mysqld05:27:18 PM 15362 2 0 php-cgi05:27:18 PM 15395 702 0 pidstat 05:27:18 PM PID minflt-nr majflt-nr Command05:27:20 PM 7114 162 0 mysqld05:27:20 PM 15359 2 0 php-cgi05:27:20 PM 15360 2 0 php-cgi05:27:20 PM 15395 702 0 pidstat 05:27:20 PM PID minflt-nr majflt-nr Command05:27:22 PM 7114 16 0 mysqld05:27:22 PM 15360 2 0 php-cgi05:27:22 PM 15361 2 0 php-cgi05:27:22 PM 15362 1 0 php-cgi05:27:22 PM 15395 702 0 pidstat Average: PID minflt-nr majflt-nr CommandAverage: 1853 2 0 irqbalanceAverage: 7114 73 0 mysqldAverage: 7910 0 0 rpc.idmapdAverage: 15089 0 0 php-cgiAverage: 15090 0 0 php-cgiAverage: 15091 0 0 php-cgiAverage: 15359 1 0 php-cgiAverage: 15360 5 0 php-cgiAverage: 15361 1 0 php-cgiAverage: 15362 1 0 php-cgiAverage: 15395 703 0 pidstat
Where,
PID - The identification number of the task which is being monitored together with its children.
minflt-nr - Total number of minor faults made by the task and all its children, and collected during the interval of time.
majflt-nr - Total number of major faults made by the task and all its children, and collected during the interval of time.
Type the following command:
# pidstat -T CHILD -u 2 2
Sample outputs:
Linux 2.6.32-279.el6.x86_64 (server1.cyberciti.biz) 08/21/2012 _x86_64_(8 CPU) 05:32:50 PM PID usr-ms system-ms guest-ms Command05:32:52 PM 4 0 410 0 ksoftirqd/005:32:52 PM 7114 40 10 0 mysqld05:32:52 PM 15424 10 30 0 pidstat05:32:52 PM 48440 0 10 0 memcached 05:32:52 PM PID usr-ms system-ms guest-ms Command05:32:54 PM 4 0 220 0 ksoftirqd/005:32:54 PM 7114 10 20 0 mysqld05:32:54 PM 15424 10 20 0 pidstat05:32:54 PM 48440 10 0 0 memcached Average: PID usr-ms system-ms guest-ms CommandAverage: 4 0 315 0 ksoftirqd/0Average: 7114 25 15 0 mysqldAverage: 15424 10 25 0 pidstatAverage: 48440 5 5 0 memcached
When reporting global statistics for tasks and all their children, the following values are displayed:
PID - The identification number of the task which is being monitored together with its children.
usr-ms - Total number of milliseconds spent by the task and all its children while executing at the user level (application), with or without nice priority, and collected during the interval of time. Note that this field does NOT include time spent running a virtual processor.
system-ms - Total number of milliseconds spent by the task and all its children while executing at the system level (kernel), and collected during the interval of time.
guest-ms - Total number of milliseconds spent by the task and all its children in virtual machine (running a virtual processor).
Command - The command name of the task which is being monitored together with its children.
This command has many more options, please go through man page for more info:
$ man pidstat
iostat Command - See Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS)
mpstat Command - See CPU (processors) related statistics.
sar command and kSar tool - Identifying Linux server bottlenecks with sar and kSar. man pages - pidstat(1),top(1), ps(1), and vmstat(8)
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