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Linux: Parse an IP Address

How do I parse my Linux servers IP address using a Bash shell?
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CentOS / Redhat: Turn On SELinux Protection

SELinux enforces the idea that programs should be limited in what files they can access and what actions they can take. However, by default it is turned off under RHEL / CentOS 5.x server? How do I turn it on? How can I enable SELinux on CentOS / RHEL 6 IBM server?
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Linux: Find Out The Groups A User Is In

How do I find out group membership for each user? How do I find out which users are in a group called sales?
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Linux: Find Files By Date

How do I find file by date under UNIX and Linux?
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Existing lock /var/run/yum.pid: another copy is running as pid 523.

I‘m running the command yum update -y and getting the following error:

Loaded plugins: fastestmirror, priorities
Existing lock /var/run/yum.pid: another copy is running as pid 523.
Another app is currently holding the yum lock; waiting for it to exit…

The other application is: yum-updatesd-he
Memory : 14 M RSS ( 26 MB VSZ)
Started: Tue Feb 9 08:19:02 2010 – 14 day(s) 11:47:39 ago
State : Sleeping, pid: 523
Another app is currently holding the yum lock; waiting for it to exit…
The other application is: yum-updatesd-he
Memory : 14 M RSS ( 26 MB VSZ)
Started: Tue Feb 9 08:19:02 2010 – 14 day(s) 11:47:41 ago
State : Sleeping, pid: 523

How do I fix this problem?
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Search Multiple Words / String Pattern Using grep Command on Bash shell

How do I search multiple strings or words using the grep command? For example I’d like to search word1, word2, word3 and so on within /path/to/file. How do I force grep to search multiple words? How can I grep for multiple patterns on Linux, OS X, FreeBSD, or Unix-like system?
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List The Contents Of a tar.bz2 Tarball File

How do I list the contents of a tar.bz2 file under Linux or UNIX-linke operating systems using a shell prompt?
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Determine / Find ethernet connection speed

Q. How do I determine my Ethernet connection speed under Debian Linux 4.0 server?

A. You need to use ethtool command todisplay or change ethernet card settings. It is used for querying settings of an ethernet device such as
=> Link speed

=> Autonegotiation

=> Coalescing settings

=> Change the rx/tx ring parameters

=> Setup new speed and much more

Most intelligent network devices use an autonegotiation protocol to communicate what media technologies they support, and then select the
fastest mutually supported media technology.

How do I determine ethernet connection speed?

Type the following command to get speed for eth0:
$ ethtool eth0 | less
OR
$ ethtool eth0 | grep -i speed

Bash Grep Subdirectories (Recursively)

How do I recursively grep through all sub-directories and find files containing given text / string or words?
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How to Find out the IP address assigned to eth0 and display IP only

Q. I need to get the IP address assigned to eth0 Linux interface. How do I find out IP address only? I don’t want other information displayed by Linux ifconfig command.

A. For shell script or may be for other cause you may need the IP address only. You can use ifconfig command with grep and other filters.

Default output of /sbin/ifconfig command is all interfaces:
$ /sbin/ifconfigOutput:

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:69527 errors:0 dropped:0 overruns:0 frame:0
          TX packets:69527 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:41559546 (39.6 MiB)  TX bytes:41559546 (39.6 MiB)
eth0      Link encap:Ethernet  HWaddr 00:17:9A:0A:F6:44
          inet addr:192.168.2.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::217:9aff:fe0a:f644/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:227614 errors:0 dropped:0 overruns:0 frame:0
          TX packets:60421 errors:0 dropped:0 overruns:0 carrier:0
          collisions:272 txqueuelen:1000
          RX bytes:69661583 (66.4 MiB)  TX bytes:10361043 (9.8 MiB)
          Interrupt:17
ra0       Link encap:Ethernet  HWaddr 00:50:56:C0:00:01
          inet addr:192.168.1.2  Bcast:192.168.2.255  Mask:255.255.255.0
          inet6 addr: fe80::250:56ff:fec0:1/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1024 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1320 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

Now you just select eth0 as follows:
$ /sbin/ifconfig eth0

Now you just wanted the IP address, use grep to get the IP:
$ /sbin/ifconfig eth0| grep 'inet addr:'Output:

inet addr:192.168.2.1  Bcast:192.168.2.255  Mask:255.255.255.0

To get IP address from use cut command:
$ /sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2Output:

192.168.2.1  Bcast

Finally remove Bcast with awk
$ /sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}'
Output:

192.168.2.1

See how to read UNIX/Linux system IP address in a shell script