09-19-2001
System call are those things documented in section 2 of the manual. They are things like open(), read(), fork(), exec(). Each time any program calls any of those, a counter is incremented. vmstat is showing the increments to that counter.
Once a process starts to run, it gets to run until its timeslice runs out. But if it does something like read(), it must wait until the read finishes before it can run some more. When one process stops running for any reason, the kernel must look at the run queues to find another process to run. This operation of allowing another process to run is called a context switch. Again each time it happens, a counter is incremented and vmstat is showing the increments.
If no process is on the run queues, the kernel will repeatedly scan the run queues until a process appears there. While the kernel is scanning the run queues, the system is idle.
A high number of context switches is not good. If the kernel is context switching too often, that 10% idle could be misleading. It might actually be scanning the run queues once 10% of the time rather than looping as it waits for a runnable process.
10 More Discussions You Might Find Interesting
1. UNIX for Dummies Questions & Answers
Hi,
In the unix command, "vmstat" we get information on Page memory.
what does the "mf" - "minor fault" is?
Regards,
Anent (3 Replies)
Discussion started by: anent
3 Replies
2. UNIX for Dummies Questions & Answers
When I exeute vmstat (e.g. vmstat 30 2),
in some machines I get some wierd result as the first line.
like: -117% or 208% for CPU idle percentage.
But the second line is alright.
Could someone explain this please.
Thanks !
Chaadana (4 Replies)
Discussion started by: chaandana
4 Replies
3. UNIX for Advanced & Expert Users
Hi,
what does mean the free colomne in out put of vmstat ? is it free espace of physical memory or of swap space on hard disk ?
Thank you (4 Replies)
Discussion started by: big123456
4 Replies
4. UNIX for Dummies Questions & Answers
Hi
I wanted to collect data by using vmstat -I 60 >xxxx.txt & using my own account
It was stopped by it self after 2 hours try again same result
We want to collect day date by succession how to collect data using vmstat for day
Thank you (2 Replies)
Discussion started by: Syed_45
2 Replies
5. Solaris
This is something nowbody around me can explain:
vmstat (-S 5) shows a huge number of PI but when I try to monitor it in parallel with iostat - there is no IO activity to be seen that would correspond to this.
I have 16G RAM and 32G swap file.
I'll really appreciate if somebody can explain it.... (9 Replies)
Discussion started by: dkvent
9 Replies
6. Linux
Hi everyone,
I need to see some VM manager performance/behavior information on some Linux boxes regarding pages scanned/activation of the paging algorithm in order to get an idea if a given server needs more memory and is actually paging. In Aix servers, by using the vmstat cmd you... (1 Reply)
Discussion started by: jcpetela
1 Replies
7. Shell Programming and Scripting
Hi
I need to write a script to display VMSTAT every 5 seconds and I just need the memory columns - swap free re and just the numbers and the headers arent required.
For example
bash-3.00$ vmstat 5| awk '{print $4" "$5" "$6}'
disk faults cpu ------ This header isnt required
swap... (3 Replies)
Discussion started by: kapilk
3 Replies
8. AIX
I need some guidance on the differences in observations, not sure how significantly different are they.
Also, It would be nice to hear on the values and what the obvious tuning for performance missing.
Observation 1
ending vmstat -v 3948544 memory pages
ending vmstat -v ... (1 Reply)
Discussion started by: Snipper
1 Replies
9. Solaris
I'm trying to parse vmstat output with this:
vmstat | nawk '/0/{printf "%s\ \n", $5}'
but output is different on two sparc Solaris 10 servers, one is missing line with 'free'.
why ? (3 Replies)
Discussion started by: orange47
3 Replies
10. Linux
I m checking idle time using vmstat, below are the results
var=$(ssh wmtmgr@$hostname vmstat | tail -1 | awk '{print $15}')
89
and now im subtracting 89 with 100 & im getting expected results
expr 100 - $var
11
Now How can I get the result 11 in one line code? (4 Replies)
Discussion started by: sam@sam
4 Replies
LEARN ABOUT REDHAT
vmstat
VMSTAT(8) Linux Administrator's Manual VMSTAT(8)
NAME
vmstat - Report virtual memory statistics
SYNOPSIS
vmstat [-n] [delay [ count]]
vmstat[-V]
DESCRIPTION
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.
Options
The -n switch causes the header to be displayed only once rather than periodically.
delay is the delay between updates in seconds. If no delay is specified, only one report is printed with the average values since boot.
count is the number of updates. If no count is specified and delay is defined, count defaults to infinity.
The -V switch results in displaying version information.
FIELD DESCRIPTIONS
Procs
r: The number of processes waiting for run time.
b: The number of processes in uninterruptable sleep.
w: The number of processes swapped out but otherwise runnable. This
field is calculated, but Linux never desperation swaps.
Memory
swpd: the amount of virtual memory used (kB).
free: the amount of idle memory (kB).
buff: the amount of memory used as buffers (kB).
Swap
si: Amount of memory swapped in from disk (kB/s).
so: Amount of memory swapped to disk (kB/s).
IO
bi: Blocks sent to a block device (blocks/s).
bo: Blocks received from 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: user time
sy: system time
id: idle time
NOTES
vmstat does not require special permissions.
These reports are intended to help identify system bottlenecks. Linux vmstat does not count itself as a running process.
All linux blocks are currently 1k, except for CD-ROM blocks which are 2k.
FILES
/proc/meminfo
/proc/stat
/proc/*/stat
SEE ALSO
ps(1), top(1), free(1)
BUGS
Does not tabulate the block io per device or count the number of system calls.
AUTHOR
Written by Henry Ware <al172@yfn.ysu.edu>.
Throatwobbler Ginkgo Labs 27 July 1994 VMSTAT(8)