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I need to call a modified version of a program in /home/user_name/bin rather than the (older) version in /opt/program_name/current on a CentOS 5.3 cluster. The program creates a tcsh script using python and then executes that script.

I can overwrite the PATH to call the modified version of the program in ~/bin, such that which program_name identifies the path to ~/bin. I have done this in .bashrc, .profile, .tcshrc, and .cshrc. However, each time the tcsh is executed, environmental variables from /etc/profile are loaded and the path gets reverted to /opt/program_name/current.

These program-specific variables are set when /etc/profile.d/program_name.sh is called by /etc/profile:

# /etc/profile 
for i in /etc/profile.d/*.sh ; do
    if [ -r "$i" ]; then
        . $i
unset i

Thus, when program_name.sh is called, the corresponding script is:

# /etc/profile.d/program_name.sh
setenv PATH ${PATH}:/opt/program_name/current

How can I prevent /etc/profile from being accessed by my user account?

I do not have su access and other users are still using the older version of the software in /opt/program_name/current so I can't update the software or modify settings in /etc/profile.d/program_name.sh

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1 Answer

tcsh doesn't spontaneously read /etc/profile, there must be something in the script causing this. A likely possibility (but not the only one) is that the script starts with #!/bin/tcsh -l, so tcsh acts as a login shell. That still won't cause it to read /etc/profile, but it will cause it to read /etc/csh.login, which may read other files (I don't know what CentOS ships in csh.login nor how your system administrators have customized it).

After reading /etc/csh.login, tcsh reads ~/.login. Depending on how it's been configured, it may read ~/.login before, after, or instead of ~/.tcshrc. So be sure to try overriding PATH in ~/.tcshrc as well.

If that doesn't work, modifying the Python script may be your best bet. If the code is in a module, you may be able to work around it by putting a wrapper module in PYTHONPATH that loads the original and makes a few changes.

If that fails, there is no easy way to “redirect” the access the program executable or to tcsh. This is possible in principle by using LD_PRELOAD to wrap around a few file access functions (if all the programs involved are dynamically linked and not set[ug]id), but it's a lot of work.

There may well be an easier way by hooking into the script somewhere, e.g. overriding one of the programs called near the beginning of the script with a function defined in your .cshrc. It's difficult to be more precise without seeing that script.

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The problem of calling environmental variables when tcsh is invoked appears to be global and not limited to my script. I tried installing a local copy of tcsh in ~/bin/ and I set my PATH in ~/.bashrc ~/.profile ~/.cshrc and ~/.tcshrc to look in ~/bin before /bin. As a result, which tcsh returns /home/user_name/bin/tcsh but when i type tcsh it still loads environmental variables from elsewhere. –  David Nov 26 '12 at 16:44
@David Run strace -eopen tcsh to see what files it's reading. –  Gilles Nov 26 '12 at 17:20
strace isn't installed on the Cluster. When I run strace -eopen tcsh on the head node I get back the paths I expect. In fact, tcsh behaves as expected when I initially log into the head node. I think that connecting to the Sun Grid Cluster nodes is pulling global variables from /etc/csh.cshrc. I can't find the setenv variables specified elsewhere. /etc/csh.cshrc executes /etc/profile.d/*.csh which contains the program-specific setenv PATH ${PATH}:/opt/program_name/current calls. These variables are set every time tcsh is called, overwriting my $PATH. –  David Nov 27 '12 at 0:20
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