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Red Hat / CentOS: Swap / Change Ethernet Aliases

Q. My Ethernet aliases are randomly switched and they are bound to the wrong interface. My eth0 became eth1 and eth1 become eth0. This is causing all sort of trouble for services and firewall configurations. How do I swap back and make sure Ethernet aliases works correctly under CentOS Linux server?
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Sysadmin because even developers need heroes!!!

Setting Up a CentOS / Red Hat Linux DHCP Client

Q. How do I setup my Red Hat / CentOS / Fedora Linux system to get IP address and other information via a DHCP server for eth0 interface?
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Linux Set Up Routing with ip Command

Can you explain the ip command to setup routing on Linux based systems? How do I use the ip command to configure the routing table of the Linux kernel?
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Linux Virtual Network Interfaces Go Down When I bring Down eth0:0

Q. My RHEL / CentOS Linux 4.x virtual network interfaces go down when I bring down eth0:0. How do I fix this issue?
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Linux: Find my IP address using Perl at a shell prompt

Q. How do I find out my IP address assigned to eth0 or ra0 interface using perl?

A. If you need to know the IP address of the UNIX / Linux machine you are running on, use the following perl one liner. Perl don’t have any inbuilt facility but combination of ifconfig command ans shell pipes you can craft something as follows to display your system IP address:

Find my IP address using Perl One liner and shell pipes

Type the following command at a shell prompt:

ifconfig -a | perl -ne 'if ( m/^\s*inet (?:addr:)?([\d.]+).*?cast/ ) { print qq($1\n); exit 0; }'

Linux ntpd sendto() Bad file descriptor error and solution

Q. I’m using Red hat Enterprise Linux server. I’m getting following error in /var/log/message file:

Apr 16 16:38:02 server ntpd[22694]: sendto(10.0.77.54): Bad file descriptor
Apr 16 16:38:08 server ntpd[22694]: sendto(66.111.46.200): Bad file descriptor
Apr 16 16:38:25 server ntpd[22694]: sendto(83.133.111.7): Bad file descriptor
Apr 16 16:38:28 server ntpd[22694]: sendto(81.169.156.100): Bad file descriptor

How do I fix above errors?

A. If you are seeing Bad file descriptor errors in /var/log/messages, make sure that only one instance of ntpd is running.

Step #1: Stop ntpd

Type the following command to stop ntpd:
# /etc/init.d/ntpd stop

Step #2: kill ntpd

Type the following command to kill all instance of ntpd:
# killall ntpd

Step #3: Start ntpd

# /etc/init.d/ntpd start

Step #4: Watch log file /var/log/messages

Use tail command:
# tail -f /var/log/messages
Output:

Apr 16 16:44:35 server ntpd[17549]: Listening on interface lo, 127.0.0.1#123
Apr 16 16:44:35 server ntpd[17549]: Listening on interface eth0, 10.5.123.2#123
Apr 16 16:44:35 server ntpd[17549]: Listening on interface eth1, 71.26.1.25#123
Apr 16 16:44:35 server ntpd[17549]: kernel time sync status 0040
Apr 16 16:44:36 server ntpd[17549]: frequency initialized -58.648 PPM from /var/lib/ntp/drift
Apr 16 16:47:52 server ntpd[17549]: synchronized to LOCAL(0), stratum 10
Apr 16 16:47:52 server ntpd[17549]: kernel time sync disabled 0041
Apr 16 16:47:52 server ntpd[17549]: synchronized to 71.26.2.221, stratum 1
Apr 16 16:50:00 server ntpd[17549]: synchronized to 10.0.77.54, stratum 

OpenBSD Change, Add or Display Default Gateway

How do I change existing openbsd gateway (openbsd routing) IP address? How do I see current routing table under OpenBSD?
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Linux command to remove virtual interfaces or network aliases

Q. How do I remove virtual interfaces such as eth0:1 or eth1:1?
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Linux: How do I list all USB devices?

Q. How do I list all USB devices connected to my computer / Linux laptop?
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