5

How do I change the at command shell from sh to bash?

When running at, I recieve the message warning: commands will be executed using /bin/sh:

at 23:33                                                              
warning: commands will be executed using /bin/sh

How can I set the default shell to /bin/bash instead of /bin/sh

4

Looking at man at, it seems like you can't change the shell.

However, you could just launch your commands inside a Bash shell inside at's SH shell, like this:

at 01:23 <<< "bash -c 'notify-send \"running from $SHELL\"'"
6

You can't change the default shell of at, it is hardcoded as /bin/sh in the source.

The source code of at clarifies this, from at.c:

    /* POSIX.2 allows the shell specified by the user's SHELL environment                                                           
       variable, the login shell from the user's password database entry,                                                                
       or /bin/sh to be the command interpreter that processes the at-job.                                                               
       It also alows a warning diagnostic to be printed.  Because of the                                                                
       possible variance, we always output the diagnostic. */

    fprintf(stderr, "warning: commands will be executed using /bin/sh\n");

Implementation, from atd.c:

if (execle("/bin/sh", "sh", (char *) NULL, nenvp) != 0)

The man page conforms accordingly:

at and batch read commands from standard input or a specified file which are to be executed at a later time, using /bin/sh.

That leaves you to recompile your own copy as the only solution to meet your need.

  • 4
    Well... he could also symlink bash to /bin/xy (or any 7-character or shorter absolute pathname), and manually edit the correct /bin/sh string in the compiled at binary to be the new path (not really recommended to anyone who isn't comfortable hex-editing binaries, but possible). – mtraceur Oct 3 '16 at 1:19
  • @mtraceur Or that ;) – heemayl Oct 3 '16 at 4:29
  • 1
    @mtraceur This seems flimsy especially if the string is interned once but has multiple uses -- my point is, the source should be recompiled, rather than editing binaries – cat Oct 3 '16 at 11:48
  • @cat: +1 because that is a good-to-remember technicality in general. But in this practical case, I think if you decide to do such a hack-y solution, then the real question is: Does at actually use the string /bin/sh\0 for anything that would break if it ended up also sharing the same string literal, with this particular change? Even without looking at the source, but knowing what at does, I am fairly confident it's likely that the answer is no, it wouldn't actually be a problem. But yes, that is a possibility worth noting. – mtraceur Oct 4 '16 at 5:25

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