How do I make sudo preserve my environment variables?

Using sudo 1.7.4p4 on Solaris 5.10 and sudo 1.6.7p5 on RHEL4 u6 I can't see how to preserve my environment variables, for instance $PYTHONPATH. I've added this line to sudoers, but it doesn't make any difference:

Defaults !env_reset

Am I doing something wrong, or is the sudo installation simply not respecting the env_reset flag?

Edit: At least on Solaris, we've found that this issue depends on the shell! The standard root shell is Bourne, if we run bash under sudo (sudo bash) on the other hand, !env_preset will preserve the environment (including PATH and LD_LIBRARY_PATH). This is rather confusing behaviour I have to say.

Use carefully, there are security issues with sudo and variables.

From man sudoers I found that you should use

Defaults        env_reset
Defaults        env_keep += "PYTHONPATH OTHERVARIABLE YETANOTHER"

In Ubuntu, sudo does preserves some variables. sudo -i is more like logging in as root and then running the command. Both may be inconvenient, the former for sudo nano myfile leaves root-owned files inside your home and the latter for sudo -i nano myfile will try to open /root/myfile.

Run

sudo printenv PATH

and see what it gives. Here it gives

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/X11R6/bin

for example. Now run sudo visudo and add the line

Defaults        secure_path=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/X11R6/bin

replacing by what you found just before. Append a new path to it if you need.

About libraries:

sudo LD_LIBRARY_PATH=/usr/lib/path/to/a/safe/library your command

Linux distributions take a lot of care with PATH, and you really should be careful before playing with it. Be specially careful about adding paths like "." or /home/username, it is unsecure.

One of the dangers of adding paths is that it opens for the possibility of files on these paths getting executed by root, opening a windows in the system security that may be exploited by malicious software. There may be other dangers. Just make sure you know what you are doing. Bypassing sudo security measures may render your Solaris as safe as Windows XP.

Fiddling with sudoers is to be done with caution, as others have said.

A simpler approach for simpler cases when there are particular environment variables you want to preserve is to just pass the environment variable you want directly through sudo (this is shown as [VAR=value] in the sudo cmdline help).

See this small example where I have also demonstrated it for more than one variable.

$ export MY_V1=1
$ export MY_V2=2
$ printenv | grep MY_V
MY_V2=2
MY_V1=1
$ sudo MY_V1=$MY_V1 MY_V2=$MY_V2 printenv | grep MY_V
MY_V2=2
MY_V1=1

For the original PYTHONPATH example in the question, just use the following:

$ sudo PYTHONPATH=$PYTHONPATH python some_script.py
<script_output_here>

Creating an alias for this type of thing is handy. Like so:

$ alias sudopy='sudo PYTHONPATH=$PYTHONPATH python'