Sstrhsrtj

Perhaps a trivial question, but I found myself in the situation of needing to strip the leading space off the output of uptime and it got me wondering why it was there in the first place.

An example from a Debian Stretch EC2 instance:

admin@ip-88-88-88-88:~$ uptime

 22:14:50 up 7 min,  1 user,  load average: 1.61, 1.21, 0.60

admin@ip-88-88-88-88:~$

I thought maybe it was padding, but for what? A three-digit hour for the clock?

Because the code explicitly puts it there:

pos = sprintf(buf, " %02d:%02d:%02d ",

  realtime->tm_hour, realtime->tm_min, realtime->tm_sec);

The uptime executable calls a function called print_uptime(). This function lives in proc/whattime.c in the procps sources. The function just outputs a string built by sprint_uptime() in the same C source file which constructs the output string bit by bit.

The first bit that is added to the string is added with an initial space, as shown above.

The space has been there since at least 2002 in the procps implementation of uptime.

Note that uptime -p does not output a space:

$ uptime -p

up 8 weeks, 8 hours, 41 minutes



$ uptime --version

uptime from procps-ng 3.3.12

As noted by maxxvw, the GNU coreutils version of the utility uses a similar kind of output.

The uptime utility on BSD systems does not follow the same output format:

$ uptime

11:56PM  up 23:58, 1 user, load averages: 0.04, 0.02, 0.00

Coreutils source code is here: https://github.com/coreutils/coreutils/blob/master/src/uptime.c

As you can see, it is just as the authors decided to print it, a space before current time, two spaces after uptime, none around users connected and two spaces before load average:

fprintftime (stdout, _(" %H:%M:%S  "), tmn, 0, 0);



printf (_("up  %2d:%02d,  "), uphours, upmins);



printf (ngettext ("%lu user", "%lu users", select_plural (entries)),



printf (_(",  load average: %.2f"), avg[0]);

It's possible the present-day GNU/Linux versions of uptime are trying to be compatible with the old BSD uptime from ~1980, which used the %3d format to print the hours portion (always <= 24) of the time. The same function was used to print both the current time-of-day and the system uptime.

if (tim >= 60) {

    printf("%3d:", tim/60);

    didhrs++;

} else {

    printf("    ");

}

tim %= 60;

if (tim > 0 || didhrs) {

    printf(didhrs&&tim<10 ? "%02d" : "%2d", tim);

} else {

    printf("  ");

}

The fact that it printed sequences of spaces instead of zeroes (rather than printing nothing) may indicate the code was taken from another program where precise column positioning was needed.