Kurinchi Blogger Scribbles ... » LINUX

How to check if linux server can send out email via command line?

kurinchilamp — Thu, 15 Dec 2011 06:05:34 +0000

Method 1:

$ mail -s “Subject: Test email from linux server” info@test.com

Press the “Return” key

Enter the body part of the email

Press ctrl + D

Enter a CC email if you would like (e.g. info2@test.com)

Press ctrl + D again

Then check the mail box to see if the mail has arrived.

Method 2:

$ echo “Enter the body part of the email” | mail -s “Subject: Test email from linux server” info@test.com -c info2@test.com

Reverse DNS and Junk Email

kurinchilamp — Mon, 12 Dec 2011 13:58:45 +0000

Many email servers depend on Reverse DNS in order to identify if the mail is legit or spam. For the Reverse DNS to work correctly, two points need to be addressed
a) Look for IP address of the mail server should return its name. PTR record should be set for this
b) Reverse look on the name should return back the IP address

For example,

$ dig -x 217.83.122.34

;; ANSWER SECTION:

34.122.83.217.in-addr.arpa. 66372 IN PTR mail.example.com.

$ dig mail.example.com

;; ANSWER SECTION:

mail.example.com. 900 IN A 217.83.122.34

Check the IP address that is getting resolved matches the name that is getting returned back.

Linux: How to upgrade PHP from 5.1 to 5.2 in CentOS5?

kurinchilamp — Tue, 15 Nov 2011 06:15:37 +0000

First Check PHP version that is currently installed

$ php -version

Check Linux Version

$ cat /etc/*-release (or redhat-release)

Create a repo file with the content given below. As you can note, we are looking for package upgrade related to php only.

$ vi /etc/yum.repos.d/CentOS-phpupgrade.repo

# CentOS5-Upgrade:
# This repository is a proving grounds for packages on their way to CentOSPlus and CentOS Extras.
# They may or may not replace core CentOS packages, and are not guaranteed to function properly.
# These packages build and install, but are waiting for feedback from testers as to
# functionality and stability. Packages in this repository will come and go during the
# development period, so it should not be left enabled or used on production systems without due
# consideration.
[cent5-upgrade]
name=CentOS5 Upgrade
baseurl=http://dev.centos.org/centos/$releasever/testing/$basearch/
enabled=1
gpgcheck=1
gpgkey=http://dev.centos.org/centos/RPM-GPG-KEY-CentOS-testing
includepkgs=php*

Update the repository

$ yum update

Restart Apache server

$ service http restart

Check the PHP version that is installed

$ php -version

Check the package repository

$ rpm -qa | grep php

Linux: How to list or allow access to ports ?

kurinchilamp — Sat, 15 Oct 2011 14:54:51 +0000

SELinux is a feature that may be turned on certain servers and it can restrict access to certain ports. In order to gain access and make the ports work, you need to open those ports.

To see if SELinux is set, type

$ sestatus

To list all port, try the semanage command

$ semanage port -l

To check for a specific port that is opened

$ semanage port -l | grep 8085

To allow access to a specific port

$ semanage port -a -t http_port_t -p tcp 8085

MySQL: How to stop, start or restart mysql?

kurinchilamp — Thu, 11 Aug 2011 00:00:34 +0000

In linux, following commands are used to start/stop/restart mysql

$/etc/init.d/mysqld start
$/etc/init.d/mysqld restart
$/etc/init.d/mysqld stop

In windows, mysql runs as a service.
C:> net stop mysql
C:> net start mysql

Linux: Case sensitive MySQL table names

kurinchilamp — Thu, 21 Jul 2011 00:11:29 +0000

When transitioning MySQL database from Windows to Linux, users often encounter issues related to case-sensitiveness. Windows is case-insensitive and Linux is case-sensitive.

In such scenarios when a database call is made after the application migration happens, users often run into errors which can send them in circles between the migration servers.

Solution to this problem is to add a single line of text under my.cnf (MySQL configuration file) under [mysqld]

lower_case_table_names=1

$ whereis my.cnf
/etc/my.cnf

$ vi my.cnf
…
…
[mysqld]
lower_case_table_names=1

Common Errors related to this issue

When the application is executed, users get “table not found” errors which is an indication of this error. You can verify the error by issuing the command

$ mysqladmin -uAdmin -pPass variables

and check for the value of lower_case_table_names.

Apache: [warn] NameVirtualHost *:80 has no VirtualHosts

kurinchilamp — Sat, 25 Jun 2011 18:14:25 +0000

$ /etc/init.d/apache2 restart

After configuring Apache server settings on the name server, you may encounter a message “[warn] NameVirtualHost 192.168.1.3:80 has no VirtualHosts”

The issue may be due to more than one entry of NameVirtualHost lines in the configuration settings. You can find this out by

$ grep NameVirtual * -R
site1:NameVirtualHost *:80
site2:NameVirtualHost *:80

Linux Solution: Remove one of the occurance of the NameVirtualHost and the warning message that you receive will vanish.

Linux: How to display ONLY the directories?

kurinchilamp — Mon, 10 Jan 2011 06:22:52 +0000

To display a list of directories in Linux, issue the command

$ ls -l | egrep ‘^d’

FTP: 530 login authentication failed

kurinchilamp — Wed, 14 Jul 2010 16:01:10 +0000

In certain scenarios, users encounter above message when they try to connect to their web hosting accounting using one of their ftp programs like filezilla, ws-ftp, cuteftp, smartftp

Solutions that seemed to have worked for me

i) Host name: Try adding ftp://www.mysite.com and set the port to 21
ii) User name: Try typing username@domain.com instead of just the user name of the ftp user

Beginner: Why there are many Linux Distributions?

kurinchilamp — Sat, 05 Jun 2010 14:29:51 +0000

There are different variants of Linux in the market like RedHat, Debian, CentOS, Ubuntu, Mandrake, Suse and a Linux beginner often ponder why they call Linux distributions by various names. The kernel or the heart of all the distributions is Linux and in bringing it to different market usage different community or vendors have adopted the kernel to serve that purpose.

Some of the key differences in these distributions are listed below,

Usage: In addition to the different flavors of Linux in the market, comes the usage of Linux. Some variants are developed as Desktops and a major as servers. In addition to that, there are virtual appliances that are packaged with other applications for easy deployment across environments. The choice is many and the usage determines the choice of the Linux flavor in most cases.

Client Support: All distributions are open source – FREE for usage. Red Hat and Ubuntu are maintained by organizations which provide commercial support which bigger organizations prefer. CentOS, Debian, Fedora are maintained by volunteers.

Commands used: For an administrator it will be easy if ALL the systems in the network use the same distribution. Some commands that are used to achieve a functionality are not consistent across distributions.

Packaging: Feature enhancements, application patches, software installation and management differ from one distribution to the other making the need for the administrator to remember the subtle keys.