Linux and Unix tutorials for new and seasoned sysadmin
Linux and Unix tutorials for new and seasoned sysadmin
How do I read a text file using awk pattern scanning and text processing language under Linux / Unix like operating systems?
Q. How do I reverse lines of a file under Linux / UNIX bash shell?
A. You need to use the rev utility or command. It copies the specified files to the standard output, reversing the order of characters in every line. If no files are specified, the standard input is read.
tail -1 /etc/passwd
Output:
dnsmasq:x:111:65534:dnsmasq,,,:/var/lib/misc:/bin/false
$ tail -1 /etc/passwd | rev
Output:
eslaf/nib/:csim/bil/rav/:,,,qsamsnd:43556:111:x:qsamsnd
Q. How do I change DNS search order in Linux? In order to improve performance I need to make changes.
A. Under Linux you need to use /etc/nsswitch.conf file which is used by system databases and Name Service Switch configuration file
Various functions in the C Library need to be configured to work correctly in the local environment. Tradition ally, this was done by using files (e.g., ‘/etc/passwd’), but other nameservices (like the Network Information Service (NIS) and the Domain Name Service (DNS)) became popular, and were hacked into the C library, usually with a fixed search order.
Open /etc/nsswitch.conf file using text editor:
# vi /etc/nsswitch.conf
Look for hosts:
hosts: files dns mdns4
Set above order as per your requirement. Close and save the file.
The file /etc/host.conf contains configuration information specific to the resolver library. It should contain one configuration keyword per line, followed by appropriate configuration information.
Open /etc/host.conf file
# vi /etc/host.conf
Find order line which specifies how host lookups are to be performed. It should be followed by one or more lookup methods, separated by commas. Valid methods are bind (dns server), hosts (/etc/hosts file), and nis (old method).
order hosts,bind
Save and close the file.
See the nsswitch.conf and host.conf man pages for details.
Q. How do I Move or migrate user accounts to from old Linux server a new Cent OS Linux server including mails? This new system a fresh installation.
A. You can migrate users from old Linux server to new Linux sever with standard commands such as tar, awk, scp and others. This is also useful if you are using old Linux distribution such as Redhat 9 or Debian 2.x.
Following files/dirs are required for traditional Linux user management:
* /etc/passwd – contains various pieces of information for each user account
* /etc/shadow – contains the encrypted password information for user’s accounts and optional the password aging information.
Continue reading “Move or migrate user accounts from old Linux server to a new Linux server”
Q. Can you explain /etc/passwd file format for Linux and UNIX operating systems?
Explains Linux user account concept and related files with an example.