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The sar command can be used to provide a system activity report.
The sar command collect, report, or save UNIX / Linux system activity information. It will save selected counters in the operating system to the /var/log/sa/sadd file. From the collected data, you get lots of information about your server:
CPU utilization
Memory paging and its utilization
Network I/O, and transfer statistics
Process creation activity
All block devices activity
Interrupts/sec etc.
There are two ways to invoke sar.
sar followed by an option (without specifying a saXX data file). This will look for the current day’s saXX data file and report the performance data that was recorded until that point for the current day.
sar followed by an option, and additionally specifying a saXX data file using -f option.
This will report the performance data for that particular day. i.e XX is the day of the month.
In all the examples below, we are going to explain how to view certain performance data for the current day. To look for a specific day, add “-f /var/log/sa/saXX” at the end of the sar command.
All the sar command will have the following as the 1st line in its output.
$ sar -u
Linux 2.6.18-194.el5PAE (dev-db) 03/26/2011 _i686_ (8 CPU)
Linux 2.6.18-194.el5PAE – Linux kernel version of the system.
(dev-db) – The hostname where the sar data was collected.
03/26/2011 – The date when the sar data was collected.
_i686_ – The system architecture
(8 CPU) – Number of CPUs available on this system. On multi core systems, this indicates the total number of cores.
1. CPU Usage of ALL CPUs (sar -u)
This gives the cumulative real-time CPU usage of all CPUs. “1 3″ reports for every 1 seconds a total of 3 times. Most likely you’ll focus on the last field “%idle” to see the cpu load.
$ sar -u 1 3
Linux 2.6.18-194.el5PAE (dev-db) 03/26/2011 _i686_ (8 CPU)
01:27:32 PM CPU %user %nice %system %iowait %steal %idle
01:27:33 PM all 0.00 0.00 0.00 0.00 0.00 100.00
01:27:34 PM all 0.25 0.00 0.25 0.00 0.00 99.50
01:27:35 PM all 0.75 0.00 0.25 0.00 0.00 99.00
Average: all 0.33 0.00 0.17 0.00 0.00 99.50
Following are few variations:
sar -u Displays CPU usage for the current day that was collected until that point.
sar -u 1 3 Displays real time CPU usage every 1 second for 3 times.
sar -u ALL Same as “sar -u” but displays additional fields.
sar -u ALL 1 3 Same as “sar -u 1 3″ but displays additional fields.
sar -u -f /var/log/sa/sa10 Displays CPU usage for the 10day of the month from the sa10 file.
2. CPU Usage of Individual CPU or Core (sar -P)
If you have 4 Cores on the machine and would like to see what the individual cores are doing, do the following.
“-P ALL” indicates that it should displays statistics for ALL the individual Cores.
In the following example under “CPU” column 0, 1, 2, and 3 indicates the corresponding CPU core numbers.
$ sar -P ALL 1 1
Linux 2.6.18-194.el5PAE (dev-db) 03/26/2011 _i686_ (8 CPU)
01:34:12 PM CPU %user %nice %system %iowait %steal %idle
01:34:13 PM all 11.69 0.00 4.71 0.69 0.00 82.90
01:34:13 PM 0 35.00 0.00 6.00 0.00 0.00 59.00
01:34:13 PM 1 22.00 0.00 5.00 0.00 0.00 73.00
01:34:13 PM 2 3.00 0.00 1.00 0.00 0.00 96.00
01:34:13 PM 3 0.00 0.00 0.00 0.00 0.00 100.00
“-P 1″ indicates that it should displays statistics only for the 2nd Core. (Note that Core number starts from 0).
$ sar -P 1 1 1
Linux 2.6.18-194.el5PAE (dev-db) 03/26/2011 _i686_ (8 CPU)
01:36:25 PM CPU %user %nice %system %iowait %steal %idle
01:36:26 PM 1 8.08 0.00 2.02 1.01 0.00 88.89
Following are few variations:
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.
3. Memory Free and Used (sar -r)
This reports the memory statistics. “1 3″ reports for every 1 seconds a total of 3 times. Most likely you’ll focus on “kbmemfree” and “kbmemused” for free and used memory.
$ sar -r 1 3
Linux 2.6.18-194.el5PAE (dev-db) 03/26/2011 _i686_ (8 CPU)
07:28:06 AM kbmemfree kbmemused %memused kbbuffers kbcached kbcommit %commit kbactive kbinact
07:28:07 AM 6209248 2097432 25.25 189024 1796544 141372 0.85 1921060 88204
07:28:08 AM 6209248 2097432 25.25 189024 1796544 141372 0.85 1921060 88204
07:28:09 AM 6209248 2097432 25.25 189024 1796544 141372 0.85 1921060 88204
Average: 6209248 2097432 25.25 189024 1796544 141372 0.85 1921060 88204
Following are few variations:
sar -r
sar -r 1 3
sar -r -f /var/log/sa/sa10
4. Swap Space Used (sar -S)
This reports the swap statistics. “1 3″ reports for every 1 seconds a total of 3 times. If the “kbswpused” and “%swpused” are at 0, then your system is not swapping.
$ sar -S 1 3
Linux 2.6.18-194.el5PAE (dev-db) 03/26/2011 _i686_ (8 CPU)
07:31:06 AM kbswpfree kbswpused %swpused kbswpcad %swpcad
07:31:07 AM 8385920 0 0.00 0 0.00
07:31:08 AM 8385920 0 0.00 0 0.00
07:31:09 AM 8385920 0 0.00 0 0.00
Average: 8385920 0 0.00 0 0.00
Following are few variations:
sar -S
sar -S 1 3
sar -S -f /var/log/sa/sa10
Notes:
Use “sar -R” to identify number of memory pages freed, used, and cached per second by the system.
Use “sar -H” to identify the hugepages (in KB) that are used and available.
Use “sar -B” to generate paging statistics. i.e Number of KB paged in (and out) from disk per second.
Use “sar -W” to generate page swap statistics. i.e Page swap in (and out) per second.
5. Overall I/O Activities (sar -b)
This reports I/O statistics. “1 3″ reports for every 1 seconds a total of 3 times.
Following fields are displays in the example below.
tps – Transactions per second (this includes both read and write)
rtps – Read transactions per second
wtps – Write transactions per second
bread/s – Bytes read per second
bwrtn/s – Bytes written per second
$ sar -b 1 3
Linux 2.6.18-194.el5PAE (dev-db) 03/26/2011 _i686_ (8 CPU)
01:56:28 PM tps rtps wtps bread/s bwrtn/s
01:56:29 PM 346.00 264.00 82.00 2208.00 768.00
01:56:30 PM 100.00 36.00 64.00 304.00 816.00
01:56:31 PM 282.83 32.32 250.51 258.59 2537.37
Average: 242.81 111.04 131.77 925.75 1369.90
Following are few variations:
sar -b
sar -b 1 3
sar -b -f /var/log/sa/sa10
Note: Use “sar -v” to display number of inode handlers, file handlers, and pseudo-terminals used by the system.
