Terminal messages related to executed command replaced by “tmux” when using Zsh

Question

When I'm inside a running tmux installation and run a command that errors out, sometimes tmux will replace the name of the original command.

ie. if test is a directory, then this happens:

jameswright in ~ at portal1 via ⬢ v12.13.0           
➜ rm test                                     
tmux: cannot remove ‘test’: Is a directory

Note this behavior doesn't occur when using cp or ls. This is on Linux using Zsh. The issue does not occur when using Bash and in .tmux.conf, neither default-command nor default-shell are set.

However, if I prefix the command with env -i — as in env -i rm test — I am properly seeing rm as the command and not tmux:

➜ env -i rm test
rm: cannot remove 'test': Is a directory

Also, if I use strace to try and debug the problem -- using strace -fostrace.out rm test-- I am also correctly seeing rm instead of tmux:

➜ strace -fostrace2.out rm test
rm: cannot remove 'test': Is a directory

Any ideas as to how this could happen?

I assume the error message should be generated by the offending command, but this appears to say otherwise.

Running /bin/rm test — using the full binary path — has the same result as above.

Also, rm --help also replaces rm with tmux:

➜ rm --help
Usage: tmux [OPTION]... FILE...
Remove (unlink) the FILE(s).

  -f, --force           ignore nonexistent files and arguments, never prompt
....
....
To remove a file whose name starts with a '-', for example '-foo',
use one of these commands:
  tmux -- -foo

  tmux ./-foo

Answer 1

The issue was that the ARGV0 environment variable to tmux. In this case, it is the tmux AppImage that is setting the variable.

According to AppImage Documentation, the $ARGV0 variable is set to the name/path called to execute the AppImage. So running tmux will set ARGV0=tmux.

However, starting tmux using the absolute path to the AppImage /users/jameswright/.local/bin/tmux gives:

➜ rm test
/users/jameswright/.local/bin/tmux: cannot remove ‘test’: Is a directory

An immediate fix to this to run unset ARGV0 while in the tmux session.

This issue was fixed in the tmux AppImage repository. Otherwise, extracting the AppImage and calling the extracted binary itself will also fix the issue.

Answer 2

I don't see anything obvious in the rm source. It is interesting that it doesn't happen in bash.

See if you can reproduce by running:

/bin/rm test

Which will definitely rule out any wrapper scripts or aliases.

If it still happens, you could install strace and run, for example:

strace -fostrace.out rm test

And you may be able to look at strace.out and see if it is being passed tmux as its first argument (I think it is the first few lines).

Also perhaps check if rm --help shows tmux as well.

Another thing worth checking is: env -i rm test to rule out any environment variable causing trouble.