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There are several large collection of Linux Tips on the Internet. those are mixture of obsolete and useful tips so some work need to be done selecting valuable info from junk. Among them:

For YUM tips one can look at Yum - Linux@Duke Project Wiki

Linux Gazette regularly publishes tips column. See for example More 2 Cent Tips! LG #106

NEWS CONTENTS

Old News ;-)

[Feb 04, 2017] Restoring deleted /tmp folder

Jan 13, 2015 | cyberciti.biz

As my journey continues with Linux and Unix shell, I made a few mistakes. I accidentally deleted /tmp folder. To restore it all you have to do is:

mkdir /tmp
chmod 1777 /tmp
chown root:root /tmp
ls -ld /tmp
 
mkdir /tmp chmod 1777 /tmp chown root:root /tmp ls -ld /tmp 

[Feb 04, 2017] Use CDPATH to access frequent directories in bash - Mac OS X Hints

Feb 04, 2017 | hints.macworld.com
The variable CDPATH defines the search path for the directory containing directories. So it served much like "directories home". The dangers are in creating too complex CDPATH. Often a single directory works best. For example export CDPATH = /srv/www/public_html . Now, instead of typing cd /srv/www/public_html/CSS I can simply type: cd CSS
Use CDPATH to access frequent directories in bash UNIX
Mar 21, '05 10:01:00AM Contributed by: jonbauman

I often find myself wanting to cd to the various directories beneath my home directory (i.e. ~/Library, ~/Music, etc.), but being lazy, I find it painful to have to type the ~/ if I'm not in my home directory already. Enter CDPATH , as desribed in man bash ):

The search path for the cd command. This is a colon-separated list of directories in which the shell looks for destination directories specified by the cd command. A sample value is ".:~:/usr".
Personally, I use the following command (either on the command line for use in just that session, or in .bash_profile for permanent use):
CDPATH=".:~:~/Library"

This way, no matter where I am in the directory tree, I can just cd dirname , and it will take me to the directory that is a subdirectory of any of the ones in the list. For example:
$ cd
$ cd Documents 
/Users/baumanj/Documents
$ cd Pictures
/Users/username/Pictures
$ cd Preferences
/Users/username/Library/Preferences
etc...

[ robg adds: No, this isn't some deeply buried treasure of OS X, but I'd never heard of the CDPATH variable, so I'm assuming it will be of interest to some other readers as well.]

cdable_vars is also nice
Authored by: clh on Mar 21, '05 08:16:26PM

Check out the bash command shopt -s cdable_vars

From the man bash page:

cdable_vars

If set, an argument to the cd builtin command that is not a directory is assumed to be the name of a variable whose value is the directory to change to.

With this set, if I give the following bash command:

export d="/Users/chap/Desktop"

I can then simply type

cd d

to change to my Desktop directory.

I put the shopt command and the various export commands in my .bashrc file.

How can I find information on the maximum amount of memory my system can handle

Red Hat Knowledgebase

The dmidecode command can be used to display information from the systems' BIOS that includes the maximum memory that the BIOS will support. This information is displayed by dmidecode as type 16 (Physical Memory Array) which can be filtered with the command dmidecode -t 16.

For instance, the following output shows a system that can support a maximum of 16GB of RAM.

Handle 0x0032, DMI type 16, 15 bytes
Physical Memory Array
	Location: System Board Or Motherboard
	Use: System Memory
	Error Correction Type: None
	Maximum Capacity: 16 GB
	Error Information Handle: Not Provided
	Number Of Devices: 4

Change your Hostname without Rebooting in RedHat Linux

Written by Tony Bhimani
September 8, 2005

Requirements
RedHat Linux (should apply to 7.x and up)

This tutorial covers changing your hostname in RedHat Linux without having to do a reboot for the changes to take effect. I've tested this on RedHat 7.3, 9, Fedora Core 3, and CentOS 4.1. It should work for all the versions in between since they all closely follow the same RedHat configuration. What's the point of this tutorial? Never reboot if you don't have to and keep your uptime intact.

Make sure you are logged in as root and move to /etc/sysconfig and open the network file in vi.

cd /etc/sysconfig
vi network

Look for the HOSTNAME line and replace it with the new hostname you want to use. In this example I want to replace localhost with redhat9.

HOSTNAME=redhat9

When you are done, save your changes and exit vi. Next we will edit the /etc/hosts file and set the new hostname.

vi /etc/hosts

In hosts, edit the line that has the old hostname and replace it with your new one.

192.168.1.110		redhat9

Save your changes and exit vi. The changes to /etc/hosts and /etc/sysconfig/network are necessary to make your changes persistent (in the event of an unscheduled reboot).

Now we use the hostname program to change the hostname that is currently set.

hostname redhat9

And run it again without any parameters to see if the hostname changed.

hostname

Finally we will restart the network to apply the changes we made to /etc/hosts and /etc/sysconfig/network.

service network restart

To verify the hostname has been fully changed, logout of your system and you should see your new hostname being used at the login prompt and after you've logged back in.

Quick, painless, and you won't lose your server's uptime.