thisroot.sh can set incorrect ROOTSYS

[ClarkMcGrew]

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Description

thisroot.sh doesn't check that the found SOURCE actually contains thisroot.sh before using it to set ROOTSYS. I've checked and the relevant lines on "master" don't seem to have changed.

Reproducer

This can be reproduced from the command line using

cd  # don't be in the root source
cat [location of root]/bin/thisroot.sh | /usr/bin/dash

(substitute the path to root). On my system the exact command is:

cd
cat work/t2k/software/nd280-v14.38/ROOT_6.32.02.03/Linux-Debian_13-gcc_14-x86_64/bin/thisroot.sh | /usr/bin/dash

ROOT version

ROOT v6.32.02
Built for linuxx8664gcc on Dec 23 2025, 19:07:20
From heads/master@tags/v6-32-02
With c++ (Debian 14.2.0-19) 14.2.0
Binary directory: /home/mcgrew/work/t2k/software/nd280-v14.38/ROOT_6.32.02.03/Linux-Debian_13-gcc_14-x86_64/bin

Installation method

Built from source using T2K build wrapper

Operating system

Linux Debian 13.2

Additional context

Using thisroot.sh inside a Makefile (generated by cmake) on debian 13 where "/usr/bin/sh" is linked to "dash" causes

   x=$(lsof -p $$ -Fn0 2>/dev/null | tail -1); # Paul Brannan https://stackoverflow.com/a/42815001/7471760
   SOURCE=${x#*n}

to return /dev/pts/0 (expected since Brannan's fix isn't completely portable, and there's probably no way to make it work everyplace), leaving SOURCE pointing to /dev.

This can be handled by checking that SOURCE contains thisroot.sh. For instance, add:

   # Check to see if the right directory was found (near thisroot.sh line 238)
   if [ ! -f ${thisroot}/../bin/thisroot.sh ]; then
       echo SOURCE IS ${SOURCE}
       echo DID NOT FIND thisroot.sh at ${thisroot}/../bin
       return 1
   fi

before using ${thisroot} to set ROOTSYS. The thisroot.sh script will fail, but it doesn't leave ROOTSYS pointing to the wrong location, which is probably the best that can be hoped for on a pure posix shell and an odd setup.

[ahmedbilal9]

Hi! I'd like to work on this issue.

From what I understand, the problem occurs when lsof fails to detect the correct source location (particularly on dash shell), causing SOURCE to resolve to something like /dev/pts/0 instead of the actual script path.

My proposed fix:

• Add a validation check after SOURCE is determined
• Verify that ${thisroot}/bin/thisroot.sh exists before setting ROOTSYS
• Return an error with helpful message if validation fails

This should prevent ROOTSYS from being set to invalid paths while providing clear feedback to users.

I'll submit a PR soon. Please let me know if this approach sounds good or if you'd prefer a different solution.

[ClarkMcGrew]

From my user perspective, that's a great solution since dash (and any pure posix shell) doesn't help, and lsof doesn't have the "secret" information that bash seems to use.