Linux Performance Monitoring with Vmstat and Iostat Commands

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This is our ongoing series of Linux Commands and Linux Performance Monitoring, in this article, you will learn about Vmstat and Iostat commands, which are available on all major Unix-like (Linux/Unix/FreeBSD/Solaris) Operating Systems.

vmstat command (also known as virtual memory statistic tool) shows information about processes, memory, disk, and CPU activity in Linux, whereas the iostat command is used to monitor CPU utilization, system input/output statistics for all the disks and partitions.

If vmstat and iostat commands are not available in your Linux machine, please install the sysstat package. The vmstat, sar, and iostat commands are the collection of package included in sysstat – the system monitoring tools.

You may download and install sysstat using the source tarball from link sysstat, but we recommend installing through the package manager.

Install Sysstat in Linux

$ sudo apt install sysstat         [On Debian, Ubuntu and Mint]
$ sudo yum install sysstat         [On RHEL/CentOS/Fedora and Rocky Linux/AlmaLinux]
$ sudo emerge -a app-admin/sysstat [On Gentoo Linux]
$ sudo pacman -S sysstat           [On Arch Linux]
$ sudo zypper install sysstat      [On OpenSUSE]    
Install Sysstat in Linux
Install Sysstat in Linux

Learn Vmstat Command Examples in Linux

In this section, you will learn about 6 vmstat command examples and usage with screenshots.

1. List Active and Inactive Memory

In the below example, there are six columns. The significance of the columns are explained on the man page of vmstat in detail. The most important fields are free under memory and si, so under the swap column.

[[email protected] ~]# vmstat -a

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free  inact active   si   so    bi    bo   in   cs us sy id wa st
 1  0      0 810420  97380  70628    0    0   115     4   89   79  1  6 90  3  0
  • Free – Amount of free/idle memory spaces.
  • si – Swapped in every second from disk in KiloBytes.
  • so – Swapped out every second to disk in KiloBytes.

Note: If you run vmstat without parameters it will display a summary report since system boot.

2. Execute vmstat ‘X’ seconds and (‘Number of times)

With this command, vmstat execute every two seconds and stop automatically after executing six intervals.

[[email protected] ~]# vmstat 2 6

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 810420  22064 101368    0    0    56     3   50   57  0  3 95  2  0
 0  0      0 810412  22064 101368    0    0     0     0   16   35  0  0 100  0  0
 0  0      0 810412  22064 101368    0    0     0     0   14   35  0  0 100  0  0
 0  0      0 810412  22064 101368    0    0     0     0   17   38  0  0 100  0  0
 0  0      0 810412  22064 101368    0    0     0     0   17   35  0  0 100  0  0
 0  0      0 810412  22064 101368    0    0     0     0   18   36  0  1 100  0  0

3. Vmstat with Timestamps

vmstat command with -t parameter shows timestamps with every line printed as shown below.

[[email protected] ~]$ vmstat -t 1 5

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ ---timestamp---
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 632028  24992 192244    0    0    70     5   55   78  1  3 95  1  0        2012-09-02 14:57:18 IST
 1  0      0 632028  24992 192244    0    0     0     0  171  514  1  5 94  0  0        2012-09-02 14:57:19 IST
 1  0      0 631904  24992 192244    0    0     0     0  195  600  0  5 95  0  0        2012-09-02 14:57:20 IST
 0  0      0 631780  24992 192244    0    0     0     0  156  524  0  5 95  0  0        2012-09-02 14:57:21 IST
 1  0      0 631656  24992 192244    0    0     0     0  189  592  0  5 95  0  0        2012-09-02 14:57:22 IST

4. Statistics of Various Counter

vmstat command with -s switch displays summary of various event counters and memory statistics.

[[email protected] ~]$ vmstat -s

      1030800  total memory
       524656  used memory
       277784  active memory
       185920  inactive memory
       506144  free memory
        26864  buffer memory
       310104  swap cache
      2064376  total swap
            0  used swap
      2064376  free swap
         4539 non-nice user cpu ticks
            0 nice user cpu ticks
        11569 system cpu ticks
       329608 idle cpu ticks
         5012 IO-wait cpu ticks
           79 IRQ cpu ticks
           74 softirq cpu ticks
            0 stolen cpu ticks
       336038 pages paged in
        67945 pages paged out
            0 pages swapped in
            0 pages swapped out
       258526 interrupts
       392439 CPU context switches
   1346574857 boot time
         2309 forks

5. Monitor Linux Disks Statistics

vmstat with -d option display all disks statistics of Linux.

[[email protected] ~]$ vmstat -d

disk- ------------reads------------ ------------writes----------- -----IO------
       total merged sectors      ms  total merged sectors      ms    cur    sec
ram0       0      0       0       0      0      0       0       0      0      0
ram1       0      0       0       0      0      0       0       0      0      0
ram2       0      0       0       0      0      0       0       0      0      0
ram3       0      0       0       0      0      0       0       0      0      0
ram4       0      0       0       0      0      0       0       0      0      0
ram5       0      0       0       0      0      0       0       0      0      0
ram6       0      0       0       0      0      0       0       0      0      0
ram7       0      0       0       0      0      0       0       0      0      0
ram8       0      0       0       0      0      0       0       0      0      0
ram9       0      0       0       0      0      0       0       0      0      0
ram10      0      0       0       0      0      0       0       0      0      0
ram11      0      0       0       0      0      0       0       0      0      0
ram12      0      0       0       0      0      0       0       0      0      0
ram13      0      0       0       0      0      0       0       0      0      0
ram14      0      0       0       0      0      0       0       0      0      0
ram15      0      0       0       0      0      0       0       0      0      0
loop0      0      0       0       0      0      0       0       0      0      0
loop1      0      0       0       0      0      0       0       0      0      0
loop2      0      0       0       0      0      0       0       0      0      0
loop3      0      0       0       0      0      0       0       0      0      0
loop4      0      0       0       0      0      0       0       0      0      0
loop5      0      0       0       0      0      0       0       0      0      0
loop6      0      0       0       0      0      0       0       0      0      0
loop7      0      0       0       0      0      0       0       0      0      0
sr0        0      0       0       0      0      0       0       0      0      0
sda     7712   5145  668732  409619   3282  28884  257402  644566      0    126
dm-0   11578      0  659242 1113017  32163      0  257384 8460026      0    126
dm-1     324      0    2592    3845      0      0       0       0      0      2

6. Display Statistics in Megabytes

The vmstat displays memory statistics in kilobytes by default, but you can also display reports with memory sizes in megabytes with the argument -S M. Consider the following example.

[[email protected] ~]# vmstat -S M 1 5

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0    346     53    476    0    0    95     8   42   55  0  2 96  2  0
 0  0      0    346     53    476    0    0     0     0   12   15  0  0 100  0  0
 0  0      0    346     53    476    0    0     0     0   32   62  0  0 100  0  0
 0  0      0    346     53    476    0    0     0     0   15   13  0  0 100  0  0
 0  0      0    346     53    476    0    0     0     0   34   61  0  1 99  0  0

Learn Iostat Command Examples in Linux

In this section, you will learn about 6 iostat command examples and usage with screenshots.

7. Display CPU and I/O Statistics of Disks

iostat without arguments displays CPU and I/O statistics of all partitions as shown below.

[[email protected] ~]# iostat

Linux 2.6.32-279.el6.i686 (tecmint.com)         09/03/2012      _i686_  (1 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.12    0.01    1.54    2.08    0.00   96.24

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               3.59       161.02        13.48    1086002      90882
dm-0              5.76       159.71        13.47    1077154      90864
dm-1              0.05         0.38         0.00       2576          0

8. Shows Linux CPU Statistics

iostat with -c arguments displays only CPU statistics as shown below.

[[email protected] ~]# iostat -c

Linux 2.6.32-279.el6.i686 (tecmint.com)         09/03/2012      _i686_  (1 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.12    0.01    1.47    1.98    0.00   96.42

9. Shows Linux Disks I/O Statistics

iostat with -d arguments display only disk I/O statistics of all partitions as shown.

[[email protected] ~]# iostat -d

Linux 2.6.32-279.el6.i686 (tecmint.com)         09/03/2012      _i686_  (1 CPU)

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               3.35       149.81        12.66    1086002      91746
dm-0              5.37       148.59        12.65    1077154      91728
dm-1              0.04         0.36         0.00       2576          0

10. Shows I/O Statistics of Specific Device

By default, it displays statistics of all partitions, with -p and device name arguments display only disks I/O statistics for specific device only as shown.

[[email protected] ~]# iostat -p sda

Linux 2.6.32-279.el6.i686 (tecmint.com)         09/03/2012      _i686_  (1 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.11    0.01    1.44    1.92    0.00   96.52

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               3.32       148.52        12.55    1086002      91770
sda1              0.07         0.56         0.00       4120         18
sda2              3.22       147.79        12.55    1080650      91752

11. Display LVM Statistics

With -N (Uppercase) parameter displays only LVM statistics as shown.

[[email protected] ~]# iostat -N

Linux 2.6.32-279.el6.i686 (tecmint.com)         09/03/2012      _i686_  (1 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.11    0.01    1.39    1.85    0.00   96.64

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               3.20       142.84        12.16    1086002      92466
vg_tecmint-lv_root     5.13       141.68        12.16    1077154      92448
vg_tecmint-lv_swap     0.04         0.34         0.00       2576          0

12. Check Iostat Version

With -V (Uppercase) parameter display version of iostat as shown.

[[email protected] ~]# iostat -V

sysstat version 11.7.3
(C) Sebastien Godard (sysstat  orange.fr)

The vmstat and iostat contain a number of columns and flags which may not possible to explain in detail. If you want to know more about it you may refer man page of vmstat and iostat.

# man vmstat
# man iostat

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