Select all files but one on linux

My friend wanted to know how to select all files but one on the CLI or in a bash script. This is how I normally do it, do you know a better way?

From the command line

ls * | grep -v [pattern to ignore]

or

ls [!pattern to ignore]  *

in a bash script it may look like this,

for i in `ls * | grep -v [pattern to ignore]`
do
   do something here
done

How to find files in linux

Need to find files older than certain time frame? This will help, “find [dir] -type f -mtime +[24hours*n] ”
Examples,
Show files older than 7 days

find /tmp/ -type f -mtime +7

Show files older than 7 days and rm them.

find /tmp/ -type f -mtime +7 -exec rm {} ;

or if you have a large number of files

find /tmp/ -type f -mtime +7 | xargs rm

How to remove ^M character with VI

This is how you remove those annoying ^M characters that show up in files previously edited on a Windows/DOS platform.
In VI,

:%s/[ctrlkey+v and ctrl-key+M]//g

actual command,

:%s/^V^M//g

Here’s a walk through video I made. My first actually

How to increase file descriptors max limit on Linux

Today my DBA reported that the server she was working on was spitting out “too many open files” errors and no new processes could be started.
This is a common problem with DB servers with heavy transactions. In my environment there are 6 DB instances running on the server. No quite the optimized setup I would say.
The fix was to increase the total file descriptors kernel parameter count in the /etc/sysctl.conf file. I doubled my limit from 8192 to 16384.
The walk through,
1. Find out what the current open file descriptor limit is.

~# more /proc/sys/fs/file-max

~# 8192

or

~# sysctl -a | grep fs.file-max

~# fs.file-max = 8192

2. View how many open file descriptors are currently being used.

~# more /proc/sys/fs/file-nr

~# 8191

3. View how many files are open. The number returned might defer as 1 file descriptor can have multiple open files attached to it.

~# lsof | wc -l

~# 10325

4. Edit the kernel paramneter file /etc/sysctl.conf and add line “fs.file-max=[new value]” to it.

~# vi /etc/sysctl.conf

fs.file-max = 331287

5. Apply the changes.

~# sysctl -p
~# fs.file-max = 331287

Problem fixed.

How to set default session timeout in Linux

My DC operation guys access Linux servers on a daily basis but somehow they never remember to log out. This is a security risk as anyone could gain access to the open console and create caos.
Today, yet again I’m forced to play the bad guy by dummy proofing my Linux servers by implementing default timeout for user sessions.
Bash and Korn both support the TMOUT variable which I will use to set the default timeout.
The etc/.bashrc file will apply the timeout system wide but if you need it to be user specific then modify the ~/.bashrc file instead.
Here’s how it’s done.

echo "TMOUT=300 >> /etc/bashrc

echo "readonly TMOUT" >> /etc/bashrc

echo "export TMOUT" >> /etc/bashrc

Log off, start a new session and wait for 5 minutes. Your session should terminate

How to keep your Linux session alive

Recently I wrote about implementing session timeouts on Linux. For admin’s who know what they are doing(most times) this can sometimes be an annoying experience.
There’s a simple noop script over at bashcurescancer to help work around session timeouts. This will work for ssh and also the default virtual consoles.

Watch noop in action.



Source: BashCuresCancer

How to change the system date in Linux

A friend needed help changing the system date on his Linux box today. This is usually a simple task for Linux users but newbies tend to get confused by the "date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]" line in the man page.
To simplify, this is how you do it.
Set the current date to April 7 2008 8:42:45pm.
The easy way,
#date -s "7 April 2008 20:42:45"
The harder way,
#date 040720422008.45
The break down: MM DD hh mm YYYY ss
MM = month = 04
DD = day = 07
hh = hour = 20
mm = minute = 42
YYYY = year = 2008
ss = second = 450

sample output,
[root@klmsyslog01p ~]# date -s "7 April 2008 20:42:45"
Mon Apr 7 20:42:45 MYT 2008
[root@klmsyslog01p ~]#
[root@kmmserver01p ~]# date 040720422008.45
Mon Apr 7 20:42:45 MYT 2008
[root@kmmserver01p ~]#