I don't remember what I did. But this afternoon, when I log on to the machine, none of the commands works, ls, top, cd, ssh, nothing. Has this happened to anyone before and what could be the reason? Thanks in advance.

what's weirder is that those terminals I opened earlier which have been not logged out still works. Only if I open up a new terminal and ssh to that machine, it is doing that.

Hello, nasridine!
Could you please post the results of
from one of the old terminals and a newly opened one.

The old one

/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/opt/apbs/bin:/usr/NX/bin:/home/nasridine/bin:/sbin:/home/nasridine/tinker5:/home/nasridine/software/tinker-bin:/home/nasridine/gdma-2.2.01/bin:/usr/local/src/amber10/bin:/home/nasridine/bin:/sbin:/home/nasridine/tinker5:/home/nasridine/software/tinker-bin:/home/nasridine/gdma-2.2.01/bin:/usr/local/src/amber10/bin:/home/nasridine/software/apbs-1.2-ia32/bin

The new one

/home/nasridine/bin:/sbin:/home/nasridine/tinker5:/home/nasridine/software/tinker-bin:/home/nasridine/gdma-2.2.01/bin:/usr/local/src/amber10/bin:/home/nasridine/software/apbs-1.2-ia32/bin

The path printed out with the new terminal is exactly what I have in .bash_profile.

So I added what is missing to the bash_profile and it works now.

That reminds me that I was messing with the path thing as root earlier, but I don't remember deleting anything. I looked /etc/profile and couldn't find the path /opt/apbs/bin. Where else could it be?

Are you sure "cd" failed? it is a built-in shell function for bash so that command should not have failed from a path issue.

Also are you sure you didn't make any accidental edits and saved them by mistake?

/etc/profile 's content in different distributions is different, but I know that it sets the general program paths ( /usr/local/bin:/usr/bin:/bin:/usr/games ). For custom tweaks in the PATH environment I use ~/.bashrc and ~/.bash_profile.
The path /opt/apbs/bin is not a standard Linux path, so you can't expect to find it in the default bash settings. My advice is to always keep the PATH starting in the order /usr/local/bin:/usr/bin:/bin:/opt/bin:YOUR_PATHS_HERE, unless you know what you're doing. And by the way, if you want/need to tweak root's PATHs, use /root/.bash_profile and /root/.bashrc.
Hope this answers your question.

EDIT: Perhaps when you tweaked the PATH as root earlier, you erased the initial content by using
or This will erase any content from $PATH and register only your path in it. To avoid this you can always use This will append your path to the existing value of $PATH.

I noticed that I added another path at the bottom of /etc/profile and export it. Maybe it overwrites the other paths in the file?

As for "cd" I can't remember, maybe you are right.

You are absolutely right, that was exactly what I did.

So in case this happens again and I do not have any old terminals open, what should I do to fix it?

You can use to load the default bash settings or you could use to add the essential programs to your PATH. By the way, even if the standard programs are not in your path, you can still invoke them with the full path to the program, for example you can use /bin/ls ( or /usr/bin/ls depending on your distro ) to invoke the ls command even if /bin ( or /usr/bin ) is not in your PATH.

Thanks a lot. That was very helpful!

I would advise possibly remembering that vi is usually easily locatable at "/bin/vi", then just pull up the file you edited to cause the problem in the first place.

Or whatever other editor you prefer using, nano I believe is at /usr/bin/nano if you prefer that... but it depends. /bin/vi is the best one to remember for emergency purposes.

Very good advice, thanks.