sleep is a very popular command and we can start sleep from 1 second:

# wait one second please 
sleep 1

but what the alternative if I need to wait only 0.1 second or between 0.1 to 1 second ?

  • remark: on linux or OS X sleep 0.XXX works fine , but on solaris sleep 0.1 or sleep 0.01 - illegal syntax
  • 2
    Can I ask why you want to sleep for 1ms? – Tom O'Connor Jan 15 '13 at 14:03
  • 1
    Yes of course , in my bash script I add "sleep 1" , in some lines , but script run very slowly , so after some conclusion I calculate that sleep 0.1 also bring good results and more faster About the delay , I need delay in order to solve the ssh problem in my bash script , I perform paralel ssh login to some machines by expect and without delay its will not work , As you know from my question the delay should fit both Linux and Solaris – yael Jan 15 '13 at 14:09
  • 2
    Whatever solution you choose, keep in mind that a shell script won't be very accurate in terms of timing. – scai Jan 15 '13 at 14:34
  • How about doing something that takes a very short time to execute, but does nothing.. like echo "" >/dev/null – Tom O'Connor Jan 15 '13 at 15:01
  • Good idea but how msec this command take? , I need 0.1 msec , not less then that -:) – yael Jan 15 '13 at 15:12

Bash has a "loadable" sleep which supports fractional seconds, and eliminates overheads of an external command:

$ cd bash-3.2.48/examples/loadables
$ make sleep && mv sleep sleep.so
$ enable -f sleep.so sleep


$ which sleep
$ builtin sleep
sleep: usage: sleep seconds[.fraction]
$ time (for f in `seq 1 10`; do builtin sleep 0.1; done)
real    0m1.000s
user    0m0.004s
sys     0m0.004s

The downside is that the loadables may not be provided with your bash binary, so you would need to compile them yourself as shown (though on Solaris it would not necessarily be as simple as above).

As of bash-4.4 (September 2016) all the loadables are now built and installed by default on platforms that support it, though they are built as separate shared-object files, and without a .so suffix. Unless your distro/OS has done something creative, you should be able to do instead:

  BASH_LOADABLES_PATH=$(pkg-config bash --variable=loadablesdir 2>/dev/null)  
enable -f sleep sleep

(The man page implies BASH_LOADABLES_PATH is set automatically, I find this is not the case in the official distribution as of 4.4.12. If and when it is set correctly you need only enable -f filename commandname as required.)

If that's not suitable, the next easiest thing to do is build or obtain sleep from GNU coreutils, this supports the required feature. The POSIX sleep command is minimal, older Solaris versions implemented only that. Solaris 11 sleep does support fractional seconds.

As a last resort you could use perl (or any other scripting that you have to hand) with the caveat that initialising the interpreter may be comparable to the intended sleep time:

$ perl -e "select(undef,undef,undef,0.1);"
$ echo "after 100" | tclsh
  • 2
    Ah, since you're using expect you can probably just use "after N", where N is milliseconds, directly in your script. – mr.spuratic Jan 15 '13 at 14:46
  • use usleep like @Luis Vazquez and @sebix write – Ilan.K Feb 20 '16 at 9:36

The documentation for the sleep command from coreutils says:

Historical implementations of sleep have required that number be an integer, and only accepted a single argument without a suffix. However, GNU sleep accepts arbitrary floating point numbers. See Floating point.

Hence you can use sleep 0.1, sleep 1.0e-1 and similar arguments.

  • 1
    see my remark about SOLARIS OS – yael Jan 15 '13 at 13:37
  • Did you mix up is and isn't? – scai Jan 15 '13 at 13:42
  • see my update in my quastion – yael Jan 15 '13 at 13:45
  • 1
    Yael, I think there're still one too many negatives in your question; are you sure you mean "not illegal syntax"? – MadHatter Jan 15 '13 at 14:23
  • for example - I run on solaris 10 this: # sleep 0.1 sleep: bad character in argument , about linux sleep 0.1 works fine – yael Jan 15 '13 at 14:37

Sleep accepts decimal numbers so you can break it down this like:

1/2 of a second

 sleep 0.5

1/100 of a second

sleep 0.01

So for a millisecond you would want

sleep 0.001
  • 4
    You can also drop the leading zero before the decimal point. eg. sleep .5 – Mike Causer Jun 22 '14 at 7:13
  • Except for mathforum.org/library/drmath/view/52352.html – stark Oct 27 '17 at 13:42
  • Talk about everyone else overcomplicating it... – Martin Sep 5 '18 at 7:45
  • @MikeCauser leading zeros much more readable and signal intent to the reader of the code later. also better when you actually do math. – Alexander Mills Dec 22 '18 at 6:51

Try this to determine accuracy:

    time sleep 0.5      # 500 milliseconds (1/2 of a second)
    time sleep 0.001    # 1 millisecond (1/1000 of a second)
    time sleep 1.0      # 1 second (1000 milliseconds)

Combination of mr.spuratic's solution and coles's solution.


You may simply use usleep. It takes microseconds (= 1e-6 seconds) as parameter, so to sleep 1 millisecond you would enter:

usleep 1000
  • 1
    $ usleep No command 'usleep' found, did you mean: Command 'sleep' from package 'coreutils' (main) usleep: command not found – Bulletmagnet Apr 5 '17 at 14:18
  • No, i mean usleep part of the initscripts package which is standard at least in all the Red Hat derived distributions; including at least RHEL, CentOS, Fedora, Mageia/Mandriva and SuSE. Here an example: `` `` – Luis Vazquez Jul 15 '17 at 17:14
  • 1
    Here is a sample ilustration running in CentOS 7: ``` $ which usleep /usr/bin/usleep $ rpm -qf /usr/bin/usleep initscripts-9.49.37-1.el7_3.1.x86_64 ``` To summarize: - sleep (from coreutils) works with seconds - usleep (from initscripts) works with micro-seconds – Luis Vazquez Jul 15 '17 at 17:22

I had the same problem (no shell usleep on Solaris) so I wrote my own thus:

  #include "stdio.h"
  int main(int argc, char **argv) {
     if(argc == 1) { usleep(atoi(argv[1])); }
     return 0;

Doesn't check arguments - I'd recommend a properly written one if you wanted to keep it but that (gcc usleep.c -o usleep) will get you out of a hole.

  • 1
    You could at least change that bare usleep() call to if(argc == 1) { usleep(atoi(argv[1])); } to avoid indexing outside of the bounds of the array, which can lead to any number of unexpected behaviors. – a CVn Oct 13 '16 at 15:05

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