How to check if cygwin mintty/bash is run as administrator?

Question

Problem Statement: What is the most elegant and robust way to test if Cygwin mintty bash session is "Run as adminstrator"?

Why, specifically? I have typically several mintty terminals open when using Windows (mintty does not have tabs). The most awkward is when I need to find a terminal window that I started by right-clicking "Run as administrator" when for example I want to run ping or other one-time procedure. I would like to indicate the "run as administrator"-ness of the terminal session visually (by changing the bash shell prompt variable PS1 in my start-up file ~/.bashrc).

Some quick potential solutions:

1. I can compare the value of some environmental variables. By quick look of env output there are quite many differences. It is however hard to tell which is most reliable in terms of portability to another Windows machine (perhaps running different version of Windows).
2. id, more specifically id -Gn shows different groups if run as administrator. In my Windows 7 machine I have Administrators and root groups added to the list. Again, I am not sure if this is portable.
3. I could try to write a file to a location that would fail as normal user. But I do not want to write any files to strange places - this could in some imagined scenarios be potentially destructive (e.g. failing storage media) and this seems utterly inelegant to my taste.
4. Running some Windows program that will indicate by return status or output if the command is run "as administrator". Best would be some with analogous purpose to that of UNIX id(1) command (but natively existing in Windows - or Cygwin, but without too far fetched translation of Windows system concepts to POSIX emulated concepts).

Any better or more elegant suggestions? Perhaps cygwin provides a command utility dedicated for this purpose?

Update: 97% duplicate of https://stackoverflow.com/questions/4051883/batch-script-how-to-check-for-admin-rights/ - the difference is just here using bash instead of (IMHO weird and archaic) Windows cmd.exe. Please do check the answers and commentaries there.

Answer 1

I just wrote this function for the same reason. I never know which shell has admin privileges.

function isadmin()
{
    net session > /dev/null 2>&1
    if [ $? -eq 0 ]; then echo "admin"
    else echo "user"; fi
}

It adapted from this answer https://stackoverflow.com/a/11995662/307968 for windows cmd shell. Net Session returns 0 status if you are admin.

Now I just need to change my prompt, or maybe the titlebar color....

Answer 2

The definitive answer to this question comes from the Cygwin mailing list. A process is running with Administrator rights if the user who started it is part of group 544 (Administrators). Also from the comment below by Cromax, it seems that group 114 (Local account and member of Administrator group) is also sometimes present. The test for these two groups is

id -G | grep -qE '\<(114|544)\>'

or in bash without external calls,

[[ "${GROUPS[@]}" =~ (^| )(114|544)( |$) ]]

For example,

id -G | grep -qE '\<(114|544)\>' && echo admin || echo user

In the past you also needed to check for group 0, the root group in /etc/group. But /etc/group is no longer installed in Cygwin, and should usually be removed if it's present, so it's no longer recommended to check for group 0 too.

Answer 3

I use the return value of the Windows program at. I also recreated the functionality of the PROMPTING special character \$.

# Set a white $ initially
eStyle='\[\e[0m\]$'

# If 'at' succeeds, use a red # instead
at &> /dev/null && eStyle='\[\e[0;31m\]#\[\e[0m\]'  # Use # in red

PS1='\n\[\e[0;32m\]\u@\h \[\e[0;33m\]\w\[\e[0m\]\n'"$eStyle "

Answer 4

Do something that only admin could do and test for success or fail:-

if touch c:/Users/.x ; then  echo 'ok'  ; fi

or

touch c:/Users/.x && echo ok

or

touch c:/Users/.x && \rm c:/Users/.x && echo ok

or

touch c:/Users/.x  &> /dev/null && \rm c:/Users/.x && echo you are admin

Answer 5

id -G | grep -qE '\<(544|0)\>' didn't seem to work for me, as my output had neither <> or 544 even when elevated. However, since elevation is required for writing to %WINDIR%\system32, I used that to test for elevation with a shell function:

is_elevated() { 
   [[ $(uname -o) -eq "Cygwin" ]] || return 1
   touch $WINDIR/system32/.cyg_elevated &> /dev/null
}

When applied to Steven's excellent idea of a red hash character:

is_elevated && PS1='\[\e]0;\w\a\]\n\[\e[32m\]\u@\h \[\e[33m\]\w\[\e[0m\]\n\[\e[0;31m\]#\[\e[0m\] '

Answer 6

In Msys on Windows try this (I found the accepted answer didn't work in Msys)

at &> /dev/null && echo "Running as admin" || echo "NOT running as admin"

This relies on the return code of at being zero only when running as admin.