Sar (sysstat)
In computing, `sar` (System Activity Report) is a Solaris-derived system monitor command used to report on various system loads, including CPU activity, memory/paging, device load, network, etc. Linux distributions provide `sar` through the sysstat package.
These utilities are especially useful in Cloud Computing.
Utilities
The sysstat package contains the following system performance tools:
sar- collects and reports system activity information
iostat- reports CPU utilization and disk I/O statistics
mpstat- reports global and per-processor statistics
pidstat- reports statistics for Linux tasks (processes)
sadf- displays data collected by sar in various formats
nfsiostat- reports I/O statistics for network filesystems
cifsiostat- reports I/O statistics for CIFS filesystems
The statistics reported by `sar` deal with I/O transfer rates, paging activity, process-related activities, interrupts, network activity, memory and swap space utilization, CPU utilization, kernel activities, and TTY statistics, among others. Both UP and SMP machines are fully supported.
Example usage
- CPU usage for all CPU cores on your machine
This gives the cumulative real-time CPU usage of all CPUs on your machine. "1 3" reports for every 1 seconds a total of 3 times. The most useful column/field in this report is "%idle" for the CPU load:
$ sar -u 1 3 Linux 3.8.0-30 (foobar) 11/09/13 _x86_64_ (4 CPU) 17:12:06 CPU %user %nice %system %iowait %steal %idle 17:12:07 all 7.93 0.00 4.35 0.00 0.26 87.47 17:12:08 all 13.04 0.00 4.35 0.00 0.51 82.10 17:12:09 all 11.70 0.00 4.83 0.00 0.00 83.46 Average: all 10.89 0.00 4.51 0.00 0.26 84.34
- CPU usage for all CPU core on your machine with extended output:
$ sar -u ALL 1 3 Linux 3.8.0-30 (foobar) 11/09/13 _x86_64_ (4 CPU) 17:16:04 CPU %usr %nice %sys %iowait %steal %irq %soft %guest %idle 17:16:05 all 7.87 0.00 3.30 0.00 0.25 0.00 0.00 0.00 88.58 17:16:06 all 7.75 0.00 3.88 0.00 0.26 0.00 0.00 0.00 88.11 17:16:07 all 8.46 0.00 4.87 0.00 0.26 0.00 0.00 0.00 86.41 Average: all 8.03 0.00 4.01 0.00 0.26 0.00 0.00 0.00 87.70
- CPU usage for second day of the month (Note: On some distros, the location of the
`sar`logs is stored under/var/log/sa/):
$ sar -u -f /var/log/sysstat/sa02
- CPU usage of an individual CPU or core
If you have 4 cores on your machine and would like to see what the individual cores are doing, execute the following command (note: the "-P ALL" displays statistics for all the individual cores and, in the following example, the "CPU" column has fields 0, 1, 2, and 3 and they indicate the corresponding CPU core numbers):
$ sar -P ALL 1 1 Linux 3.8.0-30 (foobar) 11/09/13 _x86_64_ (4 CPU) 17:29:05 CPU %user %nice %system %iowait %steal %idle 17:29:06 all 7.65 0.00 4.59 0.00 0.26 87.50 17:29:06 0 10.42 0.00 3.12 0.00 1.04 85.42 17:29:06 1 13.13 0.00 11.11 0.00 0.00 75.76 17:29:06 2 4.12 0.00 3.09 0.00 0.00 92.78 17:29:06 3 2.00 0.00 2.00 0.00 0.00 96.00 Average: CPU %user %nice %system %iowait %steal %idle Average: all 7.65 0.00 4.59 0.00 0.26 87.50 Average: 0 10.42 0.00 3.12 0.00 1.04 85.42 Average: 1 13.13 0.00 11.11 0.00 0.00 75.76 Average: 2 4.12 0.00 3.09 0.00 0.00 92.78 Average: 3 2.00 0.00 2.00 0.00 0.00 96.00
Or, if you only want to display the statistics for a single core, try the following (e.g., for only the second core. Note that core numbers start from 0):
$ sar -P 1 1 1 Linux 3.8.0-30 (foobar) 11/09/13 _x86_64_ (4 CPU) 19:15:36 CPU %user %nice %system %iowait %steal %idle 19:15:37 1 0.00 0.00 3.06 0.00 1.02 95.92 Average: 1 0.00 0.00 3.06 0.00 1.02 95.92
Variations of the previous commands include:
$ sar -P ALL # Displays CPU usage broken down by all cores for the current day. $ sar -P ALL 1 3 # Displays real time CPU usage for ALL cores every 1 second for 3 times (broken down by all cores). $ sar -P 1 # Displays CPU usage for core number 1 for the current day. $ sar -P 1 1 3 # Displays real time CPU usage for core number 1, every 1 second for 3 times. $ sar -P ALL -f /var/log/sa/sa10 # Displays CPU usage broken down by all cores for the 10day day of the month from sa10 file.
