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.
sar output can be used for identifying server bottlenecks. However, analyzing information provided by sar can be difficult, so use kSar, which can take sar output and plot a nice easy to understand graph over period of time.
The sar, sa1, and sa2 commands are part of sysstat package:
- sar : Displays the data.
- sa1 and sa2: Collect and store the data for later analysis. The sa2 shell script write a daily report in the /var/log/sa directory. The sa1 shell script collect and store binary data in the system activity daily data file.
- sadc - System activity data collector. You can configure various options by modifying sa1 and sa2 scripts. They are located at the following location:
- /usr/lib64/sa/sa1 (64bit) or /usr/lib/sa/sa1 (32bit) - This calls sadc to log reports to/var/log/sa/sadX format.
- /usr/lib64/sa/sa2 (64bit) or /usr/lib/sa/sa2 (32bit) - This calls sar to log reports to /var/log/sa/sarX format.
How Do I Install sar?
Type the following command:
# yum install sysstat
Loaded plugins: downloadonly, fastestmirror, priorities, : protectbase, security Loading mirror speeds from cached hostfile * addons: mirror.cs.vt.edu * base: mirror.ash.fastserv.com * epel: serverbeach1.fedoraproject.org * extras: mirror.cogentco.com * updates: centos.mirror.nac.net 0 packages excluded due to repository protections Setting up Install Process Resolving Dependencies --> Running transaction check ---> Package sysstat.x86_64 0:7.0.2-3.el5 set to be updated --> Finished Dependency Resolution Dependencies Resolved ==================================================================== Package Arch Version Repository Size ==================================================================== Installing: sysstat x86_64 7.0.2-3.el5 base 173 k Transaction Summary ==================================================================== Install 1 Package(s) Update 0 Package(s) Remove 0 Package(s) Total download size: 173 k Is this ok [y/N]: y Downloading Packages: sysstat-7.0.2-3.el5.x86_64.rpm | 173 kB 00:00 Running rpm_check_debug Running Transaction Test Finished Transaction Test Transaction Test Succeeded Running Transaction Installing : sysstat 1/1 Installed: sysstat.x86_64 0:7.0.2-3.el5 Complete!
Edit /etc/sysconfig/sysstat file specify how long to keep log files in days, maximum is a month:
# vi /etc/sysconfig/sysstat
# keep log for 28 days # the default is 7 HISTORY=28
Save and close the file.
The Default Cron Job
The default cron job is located at /etc/cron.d/sysstat:
# cat /etc/cron.d/sysstat
# run system activity accounting tool every 10 minutes */10 * * * * root /usr/lib64/sa/sa1 1 1 # generate a daily summary of process accounting at 23:53 53 23 * * * root /usr/lib64/sa/sa2 -A
Tell sadc To Report Statistics For Disks
Edit /etc/cron.d/sysstat, enter:
# vi /etc/cron.d/sysstat
Update it as follows to log all disk stats (the -d option force to log stats for each block device and the -I option force report statistics for all system interrupts)
# run system activity accounting tool every 10 minutes
*/10 * * * * root /usr/lib64/sa/sa1 -I -d 1 1 # generate a daily summary of process accounting at 23:53 53 23 * * * root /usr/lib64/sa/sa2 -A
Save and close the file. Turn on the service, enter:
# chkconfig sysstat on
# service sysstat start
Calling the system activity data collector (sadc):
How Do I Use sar? How do I View Stats?
Use the sar command to display output the contents of selected cumulative activity counters in the operating system. In this example, sar is run to get real-time reporting from the command line about CPU utilization:
# sar -u 3 10
Linux 2.6.18-164.2.1.el5 (www-03.nixcraft.in) 12/14/2009 09:49:47 PM CPU %user %nice %system %iowait %steal %idle 09:49:50 PM all 5.66 0.00 1.22 0.04 0.00 93.08 09:49:53 PM all 12.29 0.00 1.93 0.04 0.00 85.74 09:49:56 PM all 9.30 0.00 1.61 0.00 0.00 89.10 09:49:59 PM all 10.86 0.00 1.51 0.04 0.00 87.58 09:50:02 PM all 14.21 0.00 3.27 0.04 0.00 82.47 09:50:05 PM all 13.98 0.00 4.04 0.04 0.00 81.93 09:50:08 PM all 6.60 6.89 1.26 0.00 0.00 85.25 09:50:11 PM all 7.25 0.00 1.55 0.04 0.00 91.15 09:50:14 PM all 6.61 0.00 1.09 0.00 0.00 92.31 09:50:17 PM all 5.71 0.00 0.96 0.00 0.00 93.33 Average: all 9.24 0.69 1.84 0.03 0.00 88.20
- 3 = interval
- 10 = count
To view process creation statistics, enter:
# sar -c 3 10
To view I/O and transfer rate statistics, enter:
# sar -b 3 10
To view paging statistics, enter:
# sar -B 3 10
To view block device statistics, enter:
# sar -d 3 10
To view statistics for all interrupt statistics, enter:
# sar -I XALL 3 10
To view device specific network statistics, enter:
# sar -n DEV 3 10
# sar -n EDEV 3 10
To view CPU specific statistics, enter:
# sar -P ALL
# Only 1st CPU stats
# sar -P 1 3 10
To view queue length and load averages statistics, enter:
# sar -q 3 10
To view memory and swap space utilization statistics, enter:
# sar -r 3 10
# sar -R 3 10
To view status of inode, file and other kernel tables statistics, enter:
# sar -v 3 10
To view system switching activity statistics, enter:
# sar -w 3 10
To view swapping statistics, enter:
# sar -W 3 10
To view statistics for a given process called Apache with PID # 3256, enter:
# sar -x 3256 3 10
Say Hello To kSar
sar and sadf provides CLI based output. The output may confuse all new users / sys admin. So you need to use kSar which is a java application that graph your sar data. It also permit to export data to PDF/JPG/PNG/CSV. You can load data from three method : local file, local command execution, and remote command execution via SSH. kSar supports the sar output of the following OS:
- Solaris 8, 9 and 10
- Mac OS/X 10.4+
- Linux (Systat Version >= 5.0.5)
- AIX (4.3 & 5.3)
- HPUX 11.00+
Download And Install kSar
Visit the official website and grab the latest source code. Use wget to download the source code, enter:
$ wget http://ksar.atomique.net/kSar/kSar-5.0.6.zip
Use unzip command to extract files, enter:
$ unzip kSar-5.0.6.zip
How Do I Run kSar?
Make sure JAVA jdk is installed and working correctly. Type the following command to start kSar, run:
$ cd kSar-5.0.6/
$ sh run.sh
Next you will see main kSar window, and menus with two panels.
The left one will have a list of graphs available depending on the data kSar has parsed. The right window will show you the graph you have selected.
How Do I Generate sar Graphs Using kSar?
First, you need to grab sar command statistics. Type the following command to get stats, enter (type it on your server):
[server1 ]# LC_ALL=C sar -A > /tmp/sar.data.txt
# copy file to local desktop
[desktop ]$ scp email@example.com:/tmp/sar.data.txt /tmp
Click on Data > Load data from text file > Select sar.data.txt > Open button.
Now, the graph type tree is deployed in left pane and a graph has been selected:
Zoom in and out
Using the move, you can interactively zoom onto up a part of a graph. To select a zone to zoom, click on the upper left conner and while still holding the mouse but on move to the lower-right of the zone you want to zoom. To come back to unzoomed view click and drag the mouse to any corner location except a lower-right one. You can also right click and select zoom options
Understanding kSar Graphs And sar Data
I strongly recommend reading sar and sadf command man page:
$ man sar
$ man sadf
kSar graphs can be understood from the sar command man page or by reading its official documentation.
Case Study: Identifying Linux Server CPU Bottlenecks
With sar and kSar you get detailed snapshot of memory, CPU and other subsystems. For example, if CPU utilization is more than 80% for a long period of time, a CPU bottleneck is most likely occurring. Using sar -x ALL you can find out CPU eating process. The output of mpstat command (part of sysstat package itself) will also help you understand the cpu utilization. You can easily analyzing this information with kSar.
I Found CPU Bottlenecks...
Performance tuning options for the CPU are as follows:
- Make sure that no unnecessary programs are running in background. Turn off unnecessary services.
- Use cron to schedule jobs (e.g., backup) to run at off-peak hours.
- Use top and ps command to find out all non-critical background jobs / services. Make sure you lower their priority using renice command.
- Use taskset command to set a processes's CPU affinity (offload cpu) i.e. bind processes to different CPUs. For example, run MySQL database on cpu #2 and Apache on cpu # 3.
- Make sure you are using latest drivers and firmware for your server.
- If possible add additional SMP cpus to system.
- Use faster CPUs for a single-threaded application (e.g. Lighttpd web server app).
- Use more CPUs for a multi-threaded application (e.g. MySQL database server app).
- Use more computer nodes and setup a load balancer for web app.
isag - Interactive System Activity Grapher (alternate tool)
The isag command graphically displays the system activity data stored in a binary data file by a previous sar run. The isag command invokes sar to extract the data to be plotted. isag has limited set of options as compare to kSar.