How to keep a computer from answering to ping?(#18)

a simple "echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all" will do the
trick... to turn it back on, simply
"echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_all"

Customizing your directory colors.(#19)
I know a lot of you know the command ls --color. Which displays your directory with colors. But, a lot of people may not know that those colors are customizable. All you need to do is add the following line to your /etc/bashrc file.


eval `dircolors /etc/DIR_COLORS`


And then all of the color configuration can be found in the file /etc/DIR_COLORS



Frozen Xwindow(#20)
If your Xwindow freezes sometimes, here are two ways that you may try to kill your server. The first is the simple simple way of killing your X server the key combination: Ctrl+Alt+Backspace

The second way is a little more complicated, but it works most of the time. Hit Ctrl+Alt+F2 to startup a virtual console, then log in with your user name and password and run:



# ps -ax | grep startx



This will give you the PID of your Xserver. Then just kill it with:



# kill -9 PID_Number



To go back to your first console, just hit Alt-F1



Converting all files in a directory to lowercase.(#21)
#!/bin/sh
# lowerit
# convert all file names in the current directory to lower case
# only operates on plain files--does not change the name of directories
# will ask for verification before overwriting an existing file
for x in `ls`
do
if [ ! -f $x ]; then
continue
fi
lc=`echo $x | tr '[A-Z]' '[a-z]'`
if [ $lc != $x ]; then
mv -i $x $lc
fi
done

Wow. That's a long script. I wouldn't write a script to do that; instead, I would use this command:


for i in * ; do [ -f $i ] && mv -i $i `echo $i | tr '[A-Z]' '[a-z]'`;
done;

on the command line.


Script to view those compressed HOWTOs.(#22)
From a newbie to another, here is a short script that eases looking for and viewing howto documents. My howto's are in /usr/doc/faq/howto/ and are gzipped. The file names are XXX-HOWTO.gz, XXX being the subject. I created the following script called "howto" in the /usr/local/sbin directory:

#!/bin/sh
if [ "$1" = "" ]; then
ls /usr/doc/faq/howto | less
else
gunzip -c /usr/doc/faq/howto/$1-HOWTO.gz | less
fi

When called without argument, it displays a directory of the available howto's. Then when entered with the first part of the file name (before the hyphen) as an argument, it unzips (keeping the original intact) then displays the document.
For instance, to view the Serial-HOWTO.gz document, enter:

$ howto Serial



Util to clean up your logfiles.(#23)
If you're like me, you have a list with 430 subscribers, plus 100+ messages per day coming in over UUCP. Well, what's a hacker to do with these huge logs? Install chklogs, that's what. Chklogs is written by Emilio Grimaldo, grimaldo@panama.iaehv.nl, and the current version 1.8 available from ftp.iaehv.nl:/pub/users/grimaldo/chklogs-1.8.tar.gz. It's pretty self explanatory to install(you will, of course, check out the info in the doc subdirectory). Once you've got it installed, add a crontab entry like this:

# Run chklogs at 9:00PM daily.
00 21 * * * /usr/local/sbin/chklogs -m

Handy Script to Clean Up Corefiles.(#24)
Create a file called rmcores(the author calls it handle-cores) with the following in it:

#!/bin/sh
USAGE="$0 "

if [ $# != 2 ] ; then
echo $USAGE
exit
fi

echo Deleting...
find $1 -name core -atime 7 -print -type f -exec rm {} \;

echo e-mailing
for name in `find $1 -name core -exec ls -l {} \; | cut -c16-24`
do
echo $name
cat $2 | mail $name
done

And have a cron job run it every so often.

Moving directories between filesystems.Quick way to move an entire tree of files from one disk to another (#25)
(cd /source/directory && tar cf - . ) | (cd /dest/directory && tar xvfp -)

[ Change from cd /source/directory; tar....etc. to prevent possibility of trashing directory in case of disaster.]

Finding out which directories are the largest.Ever wondered which directories are the biggest on your computer? Here's how to find out.(#26)
du -S | sort -n

How do I stop my system from fscking on each reboot?(#27)
When you rebuild the kernel, the filesystem is marked as 'dirty' and so your disk will be checked with each boot. The fix is to run:

rdev -R /zImage 1

This fixes the kernel so that it is no longer convinced that the filesystem is dirty.

Note: If using lilo, then add read-only to your linux setup in your lilo config file (Usually /etc/lilo.conf)

How to avoid fscks caused by "device busy" at reboot time.(#28)
If you often get device busy errors on shutdown that leave the filesystem in need of an fsck upon reboot, here is a simple fix:
To /etc/rc.d/init.d/halt or /etc/rc.d/rc.0, add the line

mount -o remount,ro /mount.dir

for all your mounted filesystems except /, before the call to umount -a. This means if, for some reason, shutdown fails to kill all processes and umount the disks they will still be clean on reboot. Saves a lot of time at reboot for me.

How to find the biggest files on your hard-drive.(#29)


ls -l | sort +4n

Or, for those of you really scrunched for space this takes awhile but works great:

cd /
ls -lR | sort +4n

A script for cleaning up after programs that create autosave and backup files.(#30)
Here is a simple two-liner which recursively descends a directory hierarchy removing emacs auto-save (#) and backup (~) files, .o files, and TeX .log files. It also compresses .tex files and README files. I call it 'squeeze' on my system.

#!/bin/sh
#SQUEEZE removes unnecessary files and compresses .tex and README files
#By Barry tolnas, tolnas@sun1.engr.utk.edu
#
echo squeezing $PWD
find $PWD \( -name \*~ -or -name \*.o -or -name \*.log -or -name \*\#\) -exec
rm -f {} \;
find $PWD \( -name \*.tex -or -name \*README\* -or -name \*readme\* \) -exec gzip -9 {} \;

How to find out what process is eating the most memory.(#31)
ps -aux | sort +4n

-OR-
ps -aux | sort +5n

How do I find which library in /usr/lib holds a certain function?(#32)
What if you're compiling and you've missed a library that needed linking in? All gcc reports are function names... Here's a simple command that'll find what you're looking for:

for i in *; do echo $i:;nm $i|grep tgetnum 2>/dev/null;done

Where tgetnum is the name of the function you're looking for.

I compiled a small test program in C, but when I run it, I get no output!(#32)
You probably compiled the program into a binary named test, didn't you? Linux has a program called test, which tests if a certain condition is true, it never produces any output on the screen. Instead of just typing test, try: ./test