Linux vmstat command tutorial
Linux vmstat command is a useful tool for monitoring performance in Linux system. It comes standard in Ubuntu and Slackware installation. We can get information about virtual memory(vmstat is a short form of virtual memory) and some other things such as Linux processes, cpu activity and block IO.
Here is the Linux vmstat command synopsis from the manual page:
SYNOPSIS
vmstat [-a] [-n] [delay [ count]]
vmstat [-f] [-s] [-m]
vmstat [-S unit]
vmstat [-d]
vmstat [-p disk partition]
vmstat [-V]
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Let's see some options(switch) available with vmstat command and examples of the command's output.
Linux vmstat command with '-a' option runs in Ubuntu Linux:
root@ubuntu:~# vmstat -a
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free inact active si so bi bo in cs us sy id wa
2 0 7376 6228 19944 326180 0 0 19 9 162 345 4 1 94 1
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The -a option displays active/inactive memory average values since boot. Here are the meaning of all columns:
The 'procs' field has 2 columns:
- r - The number of processes waiting for run time.
- b - The number of processes in uninterruptible sleep (blocked processes).
The 'memory' field has 4 columns:
- swpd - The amount of used swap space(virtual memory) used.
- free - The amount of idle memory(free RAM).
- inact - The amount of inactive memory.
- active - The amount of active memory.
The 'swap' field has 2 columns:
- si - Amount of memory swapped in from disk (/s).
- so - Amount of memory swapped to disk (/s).
The 'io' field has 2 columns:
- bi - Blocks received from a block device (blocks in).
- bo - Blocks sent to a block device (blocks out).
The 'system' field has 2 columns:
- in - The number of interrupts per second, including the clock (System interrupts).
- cs - The number of context switches per second (Process context switches).
The 'cpu' field has only 4 columns:
- us: Time spent running non-kernel code. (user time, including nice time).
- sy: Time spent running kernel code. (system time).
- id: Time spent idle.
- wa: Time spent waiting for IO.
We can also use vmstat command with '-a' combined with other options such as in the first command synopsis. See example below:
root@ubuntu:~# vmstat -a -n 10 3
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free inact active si so bi bo in cs us sy id wa
6 0 10560 7060 20192 324916 0 1 16 8 156 331 3 1 95 1
1 0 10560 7052 20176 324956 0 0 0 4 117 206 0 0 100 0
0 0 10560 7052 20200 324956 0 0 0 4 119 213 0 0 100 0
root@ubuntu:~#
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The vmstat example above means we want it to delay 10 seconds before the next update and count the update 3 times. The '-n' option is used so that the header does not displayed in every update.
Linux vmstat command with '-f' option runs in Ubuntu Linux:
root@ubuntu:~# vmstat -f
10109 forks
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The -f option prints the number of forks since boot.
Linux vmstat command with '-s' option runs in Ubuntu Linux:
root@ubuntu:~# vmstat -s
504628 K total memory
497548 K used memory
325892 K active memory
19284 K inactive memory
7080 K free memory
9812 K buffer memory
80136 K swap cache
995988 K total swap
12512 K used swap
983476 K free swap
104488 non-nice user cpu ticks
321 nice user cpu ticks
27624 system cpu ticks
2521995 idle cpu ticks
22965 IO-wait cpu ticks
240 IRQ cpu ticks
1121 softirq cpu ticks
0 stolen cpu ticks
349578 pages paged in
204564 pages paged out
309 pages swapped in
3378 pages swapped out
4377716 interrupts
9386803 CPU context switches
1257512796 boot time
10114 forks
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The -s option prints a table of various event counters and memory statistics.
Linux vmstat command with '-m' option runs in Ubuntu Linux:
root@ubuntu:~# vmstat -m
Cache Num Total Size Pages
RAWv6 23 23 704 23
TCPv6 24 24 1344 12
ext3_inode_cache 2994 4448 496 16
ext3_xattr 0 0 48 85
journal_handle 340 340 24 170
journal_head 147 219 56 73
revoke_record 512 512 16 256
kmalloc_dma-512 16 16 512 16
sgpool-128 24 24 2560 12
sgpool-64 24 24 1280 12
sgpool-32 24 24 640 12
scsi_io_context 0 0 104 39
fuse_request 21 21 376 21
fuse_inode 18 18 448 18
flow_cache 0 0 80 51
mqueue_inode_cache 14 14 576 14
hugetlbfs_inode_cache 23 23 344 23
dquot 0 0 128 32
shmem_inode_cache 5146 5148 448 18
xfrm_dst_cache 24 24 320 12
TCP 26 26 1216 13
Cache Num Total Size Pages
blkdev_queue 39 39 1200 13
blkdev_requests 48 80 200 20
biovec-256 10 10 3072 10
biovec-128 23 42 1536 21
biovec-64 44 63 768 21
sock_inode_cache 588 588 384 21
file_lock_cache 78 78 104 39
Acpi-Operand 1713 1734 40 102
taskstats 24 24 328 12
page_cgroup 87220 87890 24 170
proc_inode_cache 68 176 368 22
sigqueue 56 56 144 28
radix_tree_node 2273 3432 296 13
bdev_cache 32 32 512 16
sysfs_dir_cache 14684 14705 48 85
inode_cache 285 805 344 23
dentry 9863 15660 136 30
buffer_head 3948 4224 64 64
mm_struct 626 630 448 18
vm_area_struct 13378 13570 88 46
files_cache 125 147 384 21
Cache Num Total Size Pages
signal_cache 160 168 576 14
sighand_cache 146 156 1344 12
task_struct 250 260 3216 10
anon_vma 4846 4864 16 256
idr_layer_cache 595 598 152 26
kmalloc-4096 176 184 4096 8
kmalloc-2048 358 368 2048 16
kmalloc-1024 320 336 1024 16
kmalloc-512 1256 1280 512 16
kmalloc-256 105 112 256 16
kmalloc-128 759 832 128 32
kmalloc-64 4155 4480 64 64
kmalloc-32 1587 1664 32 128
kmalloc-16 3621 3840 16 256
kmalloc-8 6638 6656 8 512
kmalloc-192 5902 5985 192 21
kmalloc-96 625 672 96 42
root@ubuntu:~#
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The -m displays slabinfo.
Linux vmstat command with '-S' option runs in Ubuntu Linux:
root@ubuntu:~# vmstat -S K
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
1 0 12528 5960 11592 79112 0 0 12 7 163 347 4 1 94 1
root@ubuntu:~# vmstat -S M
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
2 0 12 5 11 77 0 0 12 7 163 347 4 1 94 1
root@ubuntu:~#
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The -S followed by k or K or m or M option outputs between 1000, 1024, 1000000, or 1048576 bytes.
Linux vmstat command with '-d' option runs in Ubuntu Linux:
root@ubuntu:~# 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
sr0 0 0 0 0 0 0 0 0 0 0
sda 26829 10390 699300 289056 27979 25655 429144 2716764 0 207
sda1 117 695 4186 852 134 3272 27256 4012 0 3
sda2 3 0 6 120 0 0 0 0 0 0
sda3 13846 5123 546682 139176 8400 3794 97608 18872 0 75
disk- ------------reads------------ ------------writes----------- -----IO------
total merged sectors ms total merged sectors ms cur sec
sda4 12775 3796 146464 147852 19445 18589 304280 2693880 0 148
sda5 67 758 1650 692 0 0 0 0 0 0
root@ubuntu:~#
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The -d reports disk statistics. Here is the meaning of all the columns available in each field:
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
That's all.
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