#vim /etc/sysconfig/network
Use something like
HOSTNAME=testarossa.maranello.local
to overwrite the default name and domain of the server.
e.g.
NETWORKING=yes HOSTNAME=testarossa.maranello.local
To avoid rebooting issue the following :
hostname testarossa.maranello.local
That will set it for the current session.
To monitor TCP and UDP connections the following command is very useful:
netstat -t -u
to have a continuous update use the watch command:
watch netstat -t -u
There is a much stronger tool for real time analysis called iptraf.
It is quite self explanatory :
at command line run
iptraf
This tool has many functions and is text mode menu ncurses based application really worth learning.
The yum message “Warning: RPMDB altered outside of yum.” or, as the yum message said for a few months, “Warning: RPMDB has been altered since the last yum transaction.” means some application has altered the rpm database (installed or removed a package) without going through the Yum APIs. This is almost always due to someone using rpm directly (Ie. rpm -ivh blah.rpm), but another possibility is an application built on top of the rpm APIs (Ie. smart, apt, zypp). While it’s possible that someone has hacked your machine and altered the rpmdb maliciously, it would have to be done poorly to trigger this warning.
There are three main sets of reasoning behind bringing this to the users attention.
There are now a few features in yum, requested by users of the package management system, that require yum is aware of all package actions on the system. Here a few of the current ones:
This is not a complete list, and as more package management features are implemented they are much more likely to be implemented at the yum layer than at the rpm layer. Not because rpm is bad, but for the same reasons that the above features were implemented in yum, it’s much easier and faster to implement them there.
# yum clean all
Setting up NTP is very important for a host of application especially clusters and applications like DBs requiring all the servers to be critically time-wise synced.
Install NTP on Red Hat and CentOS 6
$ yum install ntp
$ chkconfig ntpd on
$ ntpdate pool.ntp.org
$ service ntpd start
Install NTP on Ubuntu
The following three commands display the current routing table:
# route
Output:
Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.1.0 * 255.255.255.0 U 0 0 0 ra0 default dsl-router 0.0.0.0 UG 0 0 0 ra0
# /sbin/route
Output:
Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 191.255.255.0 * 255.255.255.0 U 0 0 0 eth0 169.254.0.0 * 255.255.0.0 U 0 0 0 eth0 default 191.255.255.1 0.0.0.0 UG 0 0 0 eth0
You can use -n option, to display numerical addresses instead of trying to determine symbolic host names (via dns or /etc/hosts file). This is useful if you are trying to determine why the route to your nameserver has vanished.$
#/sbin/route -n
Output:
Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 191.255.255.0 0.0.0.0 255.255.255.0 U 0 0 0 venet0 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 venet0 0.0.0.0 191.255.255.1 0.0.0.0 UG 0 0 0 venet0
Please note that a destionation entry 0.0.0.0 (or default) is the default gatway. In above example 191.255.255.1 is a default gatway.
The syntax is as follows:
route add default gw {IP-ADDRESS} {INTERFACE-NAME}
Where,
For example if your router IP address is 192.168.1.254 type the following command as the root user:
# route add default gw 192.168.1.254 eth0
OR use hostname such as dsl-router:
# route add default gw dsl-router eth0
If you find above command hard to use, consider using GUI tools. If your are using Red Hat/CentOS/Fedora core Linux type following command:
# redhat-config-network
OR
If you are using other Linux distribution use command:
# network-admin
Iostat is a very powerful tool for monitoring the throughput of your storage subsystems. Especially to locate bottle necks and pinpoint possible upgrade scenarios. Not immediately visible here is how to install it on Centos 5.x and 6.x.
We shall use the whatprovides tool in yum to locate the packages that provide iostat
To install vim
[root@testarossa-00-0c-29-47-8f-35 ~]# yum whatprovides vim-enhanced
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirror.crazynetwork.it
* epel: fr2.rpmfind.net
* extras: mirror.crazynetwork.it
* updates: mirror.crazynetwork.it
2:vim-enhanced-7.0.109-7.el5.i386 : A version of the VIM editor which includes
: recent enhancements.
Repo : base
Matched from:
[root@testarossa-00-0c-29-47-8f-35 ~]# yum install vim-enhanced-7.0.109-7.el5.i386
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirror.crazynetwork.it
* epel: ftp.uni-koeln.de
* extras: mirror.crazynetwork.it
* updates: mirror.crazynetwork.it
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package vim-enhanced.i386 2:7.0.109-7.el5 set to be updated
--> Processing Dependency: vim-common = 2:7.0.109-7.el5 for package: vim-enhanced
--> Running transaction check
---> Package vim-common.i386 2:7.0.109-7.el5 set to be updated
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
vim-enhanced i386 2:7.0.109-7.el5 base 1.2 M
Installing for dependencies:
vim-common i386 2:7.0.109-7.el5 base 6.4 M
Transaction Summary
================================================================================
Install 2 Package(s)
Upgrade 0 Package(s)
Total download size: 7.7 M
Is this ok [y/N]: y
Downloading Packages:
(1/2): vim-enhanced-7.0.109-7.el5.i386.rpm | 1.2 MB 00:03
(2/2): vim-common-7.0.109-7.el5.i386.rpm | 6.4 MB 00:18
--------------------------------------------------------------------------------
Total 344 kB/s | 7.7 MB 00:22
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
Installing : vim-common 1/2
Installing : vim-enhanced 2/2
Installed:
vim-enhanced.i386 2:7.0.109-7.el5
Dependency Installed:
vim-common.i386 2:7.0.109-7.el5
Complete!
[root@testarossa-00-0c-29-47-8f-35 ~]#
| Working with files | |
| Vim command | Action |
| :e filename | Open a new file. You can use the Tab key for automatic file name completion, just like at the shell command prompt. |
| :w filename | Save changes to a file. If you don’t specify a file name, Vim saves as the file name you were editing. For saving the file under a different name, specify the file name. |
| :q | Quit Vim. If you have unsaved changes, Vim refuses to exit. |
| :q! | Exit Vim without saving changes. |
| :wq | Write the file and exit. |
| : x | Almost the same as :wq, write the file and exit if you’ve made changes to the file. If you haven’t made any changes to the file, Vim exits without writing the file. |
| Moving around in the file | |
| These Vim commands and keys work both in command mode and visual mode. | |
| Vim command | Action |
| j or Up Arrow | Move the cursor up one line. |
| k or Down Arrow | Down one line. |
| h or Left Arrow | Left one character. |
| l or Right Arrow | Right one character. |
| e | To the end of a word. |
| E | To the end of a whitespace-delimited word. |
| b | To the beginning of a word. |
| B | To the beginning of a whitespace-delimited word. |
| 0 | To the beginning of a line. |
| ^ | To the first non-whitespace character of a line. |
| $ | To the end of a line. |
| H | To the first line of the screen. |
| M | To the middle line of the screen. |
| L | To the the last line of the screen. |
| :n | Jump to line number n. For example, to jump to line 42, you’d type :42 |
| Inserting and overwriting text | |
| Vim command | Action |
| i | Insert before cursor. |
| I | Insert to the start of the current line. |
| a | Append after cursor. |
| A | Append to the end of the current line. |
| o | Open a new line below and insert. |
| O | Open a new line above and insert. |
| C | Change the rest of the current line. |
| r | Overwrite one character. After overwriting the single character, go back to command mode. |
| R | Enter insert mode but replace characters rather than inserting. |
| The ESC key | Exit insert/overwrite mode and go back to command mode. |
| Deleting text | |
| Vim command | Action |
| x | Delete characters under the cursor. |
| X | Delete characters before the cursor. |
| dd or :d | Delete the current line. |
| Entering visual mode | |
| Vim command | Action |
| v | Start highlighting characters. Use the normal movement keys and commands to select text for highlighting. |
| V | Start highlighting lines. |
| The ESC key | Exit visual mode and return to command mode. |
| Editing blocks of text | |
| Note: the Vim commands marked with (V) work in visual mode, when you’ve selected some text. The other commands work in the command mode, when you haven’t selected any text. | |
| Vim command | Action |
| ~ | Change the case of characters. This works both in visual and command mode. In visual mode, change the case of highlighted characters. In command mode, change the case of the character uder cursor. |
| > (V) | Shift right (indent). |
| < (V) | Shift left (de-indent). |
| c (V) | Change the highlighted text. |
| y (V) | Yank the highlighted text. In Windows terms, “copy the selected text to clipboard.” |
| d (V) | Delete the highlighted text. In Windows terms, “cut the selected text to clipboard.” |
| yy or :y or Y | Yank the current line. You don’t need to highlight it first. |
| dd or :d | Delete the current line. Again, you don’t need to highlight it first. |
| p | Put the text you yanked or deleted. In Windows terms, “paste the contents of the clipboard”. Put characters after the cursor. Put lines below the current line. |
| P | Put characters before the cursor. Put lines above the current line. |
| Undo and redo | |
| Vim command | Action |
| u | Undo the last action. |
| U | Undo all the latest changes that were made to the current line. |
| Ctrl + r | Redo. |
| Search | |
| Vim command | Action |
| /pattern | Search the file for pattern. |
| n | Scan for next search match in the same direction. |
| N | Scan for next search match but opposite direction. |
| Replace | |
| Vim command | Action |
| :rs/foo/bar/a | Substitute foo with bar. r determines the range and a determines the arguments. |
| The range (r) can be | |
| nothing | Work on current line only. |
| number | Work on the line whose number you give. |
| % | The whole file. |
| Arguments (a) can be | |
| g | Replace all occurrences in the line. Without this, Vim replaces only the first occurrences in each line. |
| i | Ignore case for the search pattern. |
| I | Don’t ignore case. |
| c | Confirm each substitution. You can type y to substitute this match, n to skip this match, a to substitute this and all the remaining matches (“Yes to all”), and q to quit substitution. |
| Examples | |
| :452s/foo/bar/ | Replace the first occurrence of the word foo with bar on line number 452. |
| :s/foo/bar/g | Replace every occurrence of the word foo with bar on current line. |
| :%s/foo/bar/g | Replace every occurrence of the word foo with bar in the whole file. |
| :%s/foo/bar/gi | The same as above, but ignore the case of the pattern you want to substitute. This replaces foo, FOO, Foo, and so on. |
| :%s/foo/bar/gc | Confirm every substitution. |
| :%s/foo/bar/c | For each line on the file, replace the first occurrence of foo with bar and confirm every substitution. |
Original Post : Here at tuXfiles.org
The following command gives a neat list of the Devices and their IPs / details without all the gruesome details.
ifconfig | egrep "Link|inet"
A sample result would be:
[root@testarossa-00-0c-29-47-8f-35 vm]# ifconfig | egrep "Link|inet" eth0 Link encap:Ethernet HWaddr 00:0C:29:47:8F:2B inet addr:192.168.47.135 Bcast:192.168.47.255 Mask:255.255.255.0 eth1 Link encap:Ethernet HWaddr 00:0C:29:47:8F:35 inet addr:192.168.1.71 Bcast:192.168.1.255 Mask:255.255.255.0 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 peth1 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF vif0.1 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF vif4.0 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF virbr0 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0 xenbr1 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF [root@testarossa-00-0c-29-47-8f-35 vm]#
Sometimes and with some DB platforms especially when you are testing and want to reduce the number of variables during development, testing etc.. you don not want SELinux watching your back. While it is a must to enable SELinux in hardened production systems it can be quite a pain to handle. Sometimes it needs disabling (if for a short period), Here is how.
# Important
Changes you make to files while SELinux is disabled may give them an unexpected security label, and new files will not have a label. You may need to relabel part or all of the file system after re-enabling SELinux.
From the command line, you can edit the /etc/sysconfig/selinux file. This file is a symlink to/etc/selinux/config. The configuration file is self-explanatory. Changing the value of SELINUX orSELINUXTYPE changes the state of SELinux and the name of the policy to be used the next time the system boots.
[root@host2a ~]# cat /etc/sysconfig/selinux # This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - SELinux is fully disabled. SELINUX=permissive # SELINUXTYPE= type of policy in use. Possible values are: # targeted - Only targeted network daemons are protected. # strict - Full SELinux protection. SELINUXTYPE=targeted # SETLOCALDEFS= Check local definition changes SETLOCALDEFS=0
At the prompt type :
echo 0 > /selinux/enforce
Use the following procedure to change the mode of SELinux using the GUI.
# Note
You need administrator privileges to perform this procedure.
Disabled, Enforcing or Permissive, and then click OK.Enabled to Disabled or vice versa, you need to restart the machine for the change to take effect.
# Note
Changes made using this dialog box are immediately reflected in
/etc/sysconfig/selinux.