Our Blog

Latest news and updates from flathost

How SAR command work in LINUX VPS

Posted by shazim on 21 01 2017. 0 Comments

SAR stands for System Activity Report, as its name suggest sar command is used to collect,report & save CPU, Memory, I/O usage in Unix like operating system. SAR command produce the reports on the fly and can also save the reports in the log files as well.

This article explains how to install and configure sysstat package (which contains sar utility) and explains how to monitor the following Linux Vps  performance statistics using sar.

1 ) Collective CPU usage
2 ) Individual CPU statistics
3) Run queue and load average data
4 ) Swap space used and available
5 ) Report sar data from a specific time
6 ) Individual device I/O activities
7 ) Memory used and available
8 ) Context switch statistics
9 ) Network statistics
10 ) Overall I/O activities of the system

I ) How to install SAR ion LINUX

Install Sysstat Package

First, make sure the latest version of sar is available on your system. Install it using any one of the following methods depending on your distribution.

# sudo apt-get install sysstat
(or)
# yum install sysstat

 

Cheap linux vps

 

Note : Make sure to pass the option –enable-install-cron. This does the following automatically for you. If you don’t configure sysstat with this option, you have to do this ugly job yourself manually.

Creates /etc/rc.d/init.d/sysstat

 

Cheap linux vps

 

Once installed, verify the sar version using “sar -V”

Finally, make sure sar works. For example, the following gives the system CPU statistics 3 times (with 1 second interval).

 

Cheap linux vps

 

Collect the sar statistics using cron job – sa1 and sa2

 

Cheap  linux vps

Cheap  linux vps

/usr/local/lib/sa/sa1

This runs every 10 minutes and collects sar data for historical reference.

If you want to collect sar statistics every 5 minutes, change */10 to */5 in the above /etc/cron.d/sysstat file.

This writes the data to /var/log/sa/saXX file. XX is the day of the month. saXX file is a binary file. You cannot view its content by opening it in a text editor.

/usr/local/lib/sa/sa2

This runs close to midnight (at 23:53) to create the daily summary report of the sar data.

sa2 creates /var/log/sa/sarXX file (Note that this is different than saXX file that is created by sa1). This sarXX file created by sa2 is an ascii file that you can view it in a text editor.

 

Cheap linux vps

 

Linux 2.6.32-431.e16 – Linux kernel version of the system.

01/18/2017 – The date when the sar data was collected.

_x86_64_ – The system architecture

(2 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)

Cheap  linux vps

This gives the cumulative real-time CPU usage of all CPUs. “1 5” reports for every 1 seconds a total of 5 times. Most likely you’ll focus on the last field “%idle” to see the cpu load.

sar -u Displays CPU usage for the current day that was collected until that point.

sar -u 1 5 Displays real time CPU usage every 1 second for 5 times.

sar -u ALL Same as “sar -u” but displays additional fields.

sar -u ALL 1 5 Same as “sar -u 1 5” 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)

 

Cheap linux vps

 

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.

3. Memory Free and Used (sar -r)

 

Cheap linux vps

 

This reports the memory statistics. “1 5” reports for every 1 seconds a total of 5 times. Most likely you’ll focus on “kbmemfree” and “kbmemused” for free and used memory.

Following are few variations:
# sar -r
# sar -r 1 5
# sar -r -f /var/log/sa/sa10

4. Swap Space Used (sar -S)

 

Cheap linux vps

 

This reports the swap statistics. “1 5” reports for every 1 seconds a total of 5 times. If the “kbswpused” and “%swpused” are at 0, then your system is not swapping.
Following are few variations:

#sar -S
# sar -S 1 5
# sar -S -f /var/log/sa/sa10

5. Overall I/O Activities (sar -b)

Cheap linux vps

 

This reports I/O statistics. “1 5” reports for every 1 seconds a total of 5 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

Following are few variations:

# sar -b
# sar -b 1 5
# sar -b -f /var/log/sa/sa10

6. Individual Block Device I/O Activities (sar -d)

To identify the activities by the individual block devices (i.e a specific mount point, or LUN, or partition), use “sar -d”

Cheap linux vps

 

Following are few variations:

# sar -d
# sar -d 1 1
# sar -d -f /var/log/sa/sa10
# sar -p -d

7. Report network statistics (sar -n)

This reports various network statistics. For example: number of packets received (transmitted) through the network card, statistics of packet failure etc.,. “1 5” reports for every 1 seconds a total of 5 times.

# sar -n KEYWORD

KEYWORD can be one of the following:

# sar -n DEV 1 1

DEV – Displays network devices vital statistics for eth0, eth1, etc.,
EDEV – Display network device failure statistics
NFS – Displays NFS client activities
NFSD – Displays NFS server activities
SOCK – Displays sockets in use for IPv4
IP – Displays IPv4 network traffic
EIP – Displays IPv4 network errors
ICMP – Displays ICMPv4 network traffic
EICMP – Displays ICMPv4 network errors

8. Display context switch per second (sar -w)

This reports the total number of processes created per second, and total number of context switches per second. “1 5” reports for every 1 seconds a total of 5 times.

# sar -w 1 5

9. Reports run queue and load average (sar -q)

This reports the run queue size and load average of last 1 minute, 5 minutes, and 15 minutes. “1 5” reports for every 1 seconds a total of 5 times.

# sar -q 1 5

By using SAR command we can find out performance status of server .

 

Leave a Reply

Your email address will not be published.