vmstat

[root@server70 ~]# vmstat -S M 1 10
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     11    770   1009   3119    0    0    28    22   53   51  4  1 94  1  0
 3  0     11    727   1009   3120    0    0    52  2504 8387 2624 12  1 86  1  0
 0  0     11    755   1009   3120    0    0     4   157 4619 1841 12  1 86  1  0
 0  0     11    755   1009   3120    0    0   136     4 9405 1595  2  1 98  0  0
 0  0     11    755   1009   3120    0    0     0    33 4564  875  0  0 99  0  0
 1  0     11    761   1009   3120    0    0    60     0 3151 1157  2  1 97  0  0
 0  0     11    798   1009   3120    0    0    12   984 2937  898  0  0 99  0  0
 0  1     11    828   1009   3120    0    0     0   321 3108 1002  3  0 96  1  0
 0  0     11    813   1009   3120    0    0     4     0 6065 1512  6  1 93  0  0
 1  0     11    848   1009   3120    0    0     4   100 7311 1628  3  1 95  2  0
[root@server70 ~]#

vmstat 1

* High values in “wa” column mean: IO problem
* High values in “si”, “so” mean: excessive swapping

Sustained high swap rates (si and so) are usually bad. The system will start spending all of its time swapping, and make no progress on any actual work. You will also see the number of runnable (r and b) processes increase. If the situation gets bad enough and free memory gets too low, the Out-of-memory (oom) logic will start killing random processes. At this point, either reducing the number of processes that normally run or adding additional RAM are about the only options.

vmstat – Report virtual memory statistics

vmstat [-a] [-n] [delay [ count]]
vmstat [-f] [-s] [-m]
vmstat [-S unit]
vmstat [-d]
vmstat [-p disk partition]
vmstat [-V]

vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.

The first report produced gives averages since the last reboot. Additional reports give information on a sampling period of length delay. The process and memory reports are instantaneous in either case.

FIELD DESCRIPTION FOR VM MODE

   Procs
       r: The number of processes waiting for run time.
       b: The number of processes in uninterruptible sleep.

   Memory
       swpd: the amount of virtual memory used.
       free: the amount of idle memory.
       buff: the amount of memory used as buffers.
       cache: the amount of memory used as cache.
       inact: the amount of inactive memory. (-a option)
       active: the amount of active memory. (-a option)

   Swap
       si: Amount of memory swapped in from disk (/s).
       so: Amount of memory swapped to disk (/s).

   IO
       bi: Blocks received from a block device (blocks/s).
       bo: Blocks sent to a block device (blocks/s).

   System
       in: The number of interrupts per second, including the clock.
       cs: The number of context switches per second.

   CPU
       These are percentages of total CPU time.
       us: Time spent running non-kernel code. (user time, including nice time)
       sy: Time spent running kernel code. (system time)
       id: Time spent idle. Prior to Linux 2.5.41, this includes IO-wait time.
       wa: Time spent waiting for IO. Prior to Linux 2.5.41, included in idle.
       st: Time stolen from a virtual machine. Prior to Linux 2.6.11, unknown.

FIELD DESCRIPTION FOR DISK MODE

   Reads
       total: Total reads completed successfully
       merged: grouped reads (resulting in one I/O)
       sectors: Sectors read successfully
       ms: milliseconds spent reading

   Writes
       total: Total writes completed successfully
       merged: grouped writes (resulting in one I/O)
       sectors: Sectors written successfully
       ms: milliseconds spent writing

   IO
       cur: I/O in progress
       s: seconds spent for I/O

FIELD DESCRIPTION FOR DISK PARTITION MODE

       reads: Total number of reads issued to this partition
       read sectors: Total read sectors for partition
       writes : Total number of writes issued to this partition
       requested writes: Total number of write requests made for partition

FIELD DESCRIPTION FOR SLAB MODE

       cache: Cache name
       num: Number of currently active objects
       total: Total number of available objects
       size: Size of each object
       pages: Number of pages with at least one active object
       totpages: Total number of allocated pages
       pslab: Number of pages per slab

Related commands

* iostat
* sar
* mpstat
* ps
* top
* free

See Linux Commands