I want to run some things differently if I have booted into single-user/maintenance mode.
I want to know how I can test in my
.bashrc file. In particular, I would like to start
tmux only in that mode.
Where this info is found possibly varies by distro. Here's a couple of commands that may be helpful:
In Ubuntu Recovery mode (I assume this is single-user),
who -r outputs nothing, and
runlevel outputs an error
runlevel:/var/run/utmp: No such file or directory
In Ubuntu normal boot mode (multi-user), you get the following output:
$ who -r run-level 2 2015-06-27 21:41 $ runlevel N 2 $
runlevel outputs the previous run level ("N") and the current run level ("2").
systemd based systems really don't have runlevels or anything like that, what services are active can be quite more fine grained. At least Fedora retains
runlevel(8) and organizes running services into runlevels à la SysV, but that isn't mandatory.