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bug#40220: date command set linux epoch time failed

From: Bob Proulx
Subject: bug#40220: date command set linux epoch time failed
Date: Sat, 28 Mar 2020 00:52:32 -0600

tag 40220 + notabug
close 40220

shy wrote:
> I use command     date -s "1970-01-20 00:00:00" to set date, but it
>  failed.  there is error message "date: can't set date: Invalid
>  argument".
>  It's UTC time and no timezone.

This is most likely a limitation of your kernel.  I can recreate this
problem on a Linux 4.9 system for example.

  TZ=UTC strace -o /tmp/out -v date -s "1970-01-01 00:00:00"

  clock_settime(CLOCK_REALTIME, {tv_sec=0, tv_nsec=0}) = -1 EINVAL (Invalid 
  settimeofday({tv_sec=0, tv_usec=0}, NULL) = -1 EINVAL (Invalid argument)

And the documented possible returns of EINVAL for clock_settime().

       EINVAL The clk_id specified is not supported on this system.

       EINVAL (clock_settime()): tp.tv_sec is negative or tp.tv_nsec is
              outside the range [0..999,999,999].

       EINVAL (since Linux 4.3)
              A call to clock_settime() with a clk_id of CLOCK_REALTIME
              attempted to set the time to a value less than the current value
              of the CLOCK_MONOTONIC clock.

And for settimeofday().

       EINVAL (settimeofday()): timezone is invalid.

       EINVAL (settimeofday()): tv.tv_sec is negative or tv.tv_usec is outside
              the range [0..999,999].

       EINVAL (since Linux 4.3)
              (settimeofday()): An attempt was made to set the time to a value
              less than the current value of the CLOCK_MONOTONIC clock (see

       EPERM  The calling process has insufficient privilege to call
              settimeofday(); under Linux the CAP_SYS_TIME capability is

But this is not a bug in GNU date.  This is likely the effect of
CLOCK_MONOTONIC in the Linux kernel.

              Clock that cannot be set and represents monotonic time since--as
              described by POSIX--"some unspecified point in the past".  On
              Linux, that point corresponds to the number of seconds that the
              system has been running since it was booted.

              The CLOCK_MONOTONIC clock is not affected by discontinuous jumps
              in the system time (e.g., if the system administrator manually
              changes the clock), but is affected by the incremental
              adjustments performed by adjtime(3) and NTP.  This clock does
              not count time that the system is suspended.

I am not familiar with CLOCK_MONOTONIC but reading the documentation
points me to it as being the most likely reason this is not allowing
that time to be set.

I tested this in a victim system and if I was very quick I was able to
log in and set the time to :10 seconds but no earlier.

> I test with stime or settimeofday to set seconds 0, they are all have the 
> problem.
> 1. I use buildroot-2013.05, the busybox is in 1.21.1, the linux kernel is in 
> version 4.4.39.

That multiple frontends, GNU date and busybox date, all have the same
problem speaks that the problem is not with the frontend but with the
kernel handling the system call.

> 3.When set date command, the busybox uses function "stime" to set
> time, I use stime to set time around linux epoch time,
>    but the stime seems not work well.
>    int ret = 0;
>    time_t time = 20;
>    ret = stime(&time);
>    printf("ret %d %d\r\n",ret, errno);
>    perror("stime:");
> and the results are as follows:
>     ret -1 22
>     stime:: Invalid argument

And also confirmed by your independent test the the problem is not a
bug in GNU date.  Therefore I mark this GNU date bug ticket as closed
for our own accounting.  But please continue to discuss the issue


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