beer planet » unix

Do NOT Use This Perl Module: Passwd::Unix

Artem Russakovskii — Wed, 23 Apr 2008 03:05:29 +0000

Update: The author of the module contacted me the same day and promised to fix it in the next version. Version 0.40 was indeed on cpan as promised, but I haven't tested it yet.

Passwd::Unix will corrupt your /etc/shadow file and rearrange login names and their corresponding password hashes.

The current version of Passwd::Unix corrupted my /etc/shadow upon only
calling the passwd() function. Immediately users started to report not
being able to login.

After examining the situation, I found that Passwd::Unix rearranges all
users in /etc/shadow in some way, but it only does it to the
usernames, and not the password hashes. Thus, you will get corrupted accounts. Moreover,
users are now able to login to one OTHER account, not their own,
depending on how the usernames got shuffled.

Thankfully, I had a recent backup but I definitely don’t want anyone
else to suffer.

I’m using perl 5.10, SUSE 10.3. If it’s incompatible with SUSE, it needs
to say so and exit.

I've filed the bug here: http://rt.cpan.org/Public/Bug/Display.html?id=35323.

You have been warned.

How To Delete All Messages From A Folder In Pine

Artem Russakovskii — Sun, 23 Mar 2008 16:38:51 +0000

Pine is a UNIX command line mail application. So how do you delete all messages in a folder?

The combination is

; A A D

If after pressing ; you see

1	[Command ";" not defined for this screen. Use ? for help]

then you don't have a check in the "Enable aggregate command set" settings checkbox. To enable it, go to the main menu (M) -> Setup (S) -> Config (C) and scroll down to "Enable aggregate command set". Then press X (to check it), E (Exit). Now repeat the above.

Watch – A Useful Linux Command You May Have Never Heard Of

Artem Russakovskii — Sun, 05 Aug 2007 03:18:01 +0000

How many times did I want to watch a directory waiting for a file to appear in it? Constant ls, for example, quickly got boring. A quick Perl script that would reload ls every 5 seconds… yeah it works but it takes a while to type up, and often enough I'm too lazy for that. And then I found 'watch' – a utility that comes with most *nix distros. Look at this beauty [man watch]:

NAME
watch – execute a program periodically, showing output fullscreen

SYNOPSIS
watch [-dhvt] [-n ] [--differences[=cumulative]] [--help]
[--interval=] [--no-title] [--version]

DESCRIPTION
watch runs command repeatedly, displaying its output (the first screen
full). This allows you to watch the program output change over time.
By default, the program is run every 2 seconds; use -n or –interval to
specify a different interval.

The -d or –differences flag will highlight the differences between
successive updates. The –cumulative option makes highlighting
"sticky", presenting a running display of all positions that have ever
changed. The -t or –no-title option turns off the header showing the
interval, command, and current time at the top of the display, as well
as the following blank line.

watch will run until interrupted.

NOTE
Note that command is given to "sh -c" which means that you may need to
use extra quoting to get the desired effect.

Note that POSIX option processing is used (i.e., option processing
stops at the first non-option argument). This means that flags after
command don't get interpreted by watch itself.

EXAMPLES
To watch for mail, you might do

watch -n 60 from

To watch the contents of a directory change, you could use

watch -d ls -l

If you're only interested in files owned by user joe, you might use

watch -d 'ls -l | fgrep joe'

To see the effects of quoting, try these out

watch echo $$
watch echo '$$'
watch echo "'"'$$'"'"

You can watch for your administrator to install the latest kernel with

watch uname -r

(Just kidding.)

Now if anyone knows how to make watch print the bottom part of the command output rather than the top, please post a comment.

Edit: BSD users, "watch" out. watch does something completely different on BSD (it lets you snoop on other users' ttys). The corresponding BSD command is actually cmdwatch.