Tuesday, November 15, 2011

How to protect a web page with htaccess with a password

  1. Create a .htpasswd file:
    $ htpasswd -c .htpasswd <username>
  2. Create or add these lines to .htaccess file:
    • To protect a directory:
      AuthUserFile /full/path/to/.htpasswd
      AuthType Basic
      AuthName "Protected Folder"
      Require valid-user
    • To protect a file:
      AuthUserFile /full/path/to/.htpasswd
      AuthType Basic
      AuthName "Protected Page"
      <Files "protected_page.html">
        Require valid-user

Sunday, November 13, 2011

Linux Yum commands

Display available updates for installed software
$ yum list updates
Apply updates
$ yum update 
List installed packages
$ yum list installed <package-name>
# e.g.
$ yum list installed httpd
$ rpm -qa | grep httpd*

Check for and update a package
$ yum update <package-name>

Search a package or list all
$ yum list <package-name/regex/wildcard>
$ yum list all

# list group packages
$ yum grouplist

Install a package
$ yum install <package-name>

Remove/Uninstall a package
$ yum remove <package-name>

Install/Update group packages
$ yum groupinstall "Development Tools"
$ yum groupupdate "Development Tools"

List packages that are not official RHN
$ yum list extras

Find out which package is a file from
$ yum whatprovides <filename>

Wednesday, October 26, 2011

Set up shared directory in Linux

Here is how to set up a shared directory or project among linux users. The scenario is:
  • The name of the shared directory: /home/projects
  • The shared group name: developers
  • Users: john, joe, and jane

First, log in as super user, create the projects directory.
$ mkdir /home/projects

Second, create a shared group.
$ groupadd developers

Set up directory for group sharing.
# Change group on the directory
$ chgrp developers /home/projects

# Set full permission for group on the directory
$ chmod -R 775 /home/projects

# Set SGID bit on the directory so that new files under this directory will inherit the directory's group instead of the user's (creator) group.
$ chmod -R g+s /home/projects

# OR combine the last two commands into one
$ chmod -R 2775 /home/projects

# Set umask on the directory so that the 'group write' permission will be inherited on new files and directories
$ umask 002

Add users to group as supplementary group.
$ useradd -G developers john
$ useradd -G developers joe
$ useradd -G developers jane

# Check their groups
$ id john

# Add a user to multiple supplementary groups (with no space after commas):
$ useradd -G wheel,ftp,www,developers john

# Add existing user to an existing group
$ usermod -a -G wheel

# Change user's primary group
$ usermod -g developers john

You can also use this command to set the primary group for a user
$ useradd -g developers john

Saturday, October 1, 2011

htaccess Directory Listing Configurations

To prevent people from browsing your directoy, put this in your .htaccess file.
Option -indexes
IndexIgnore *

To allow people to see everything in your directory:
Option +indexes

To allow people to see everything except image files:
IndexIgnore *.gif *.jpg

How to Merge Tables

This is an example of how to insert all the missing rows from one table, tbl_backup, into another table, tbl_target. Since the primary_key is auto incremented, we will use col2 and col3 to identify unique rows.

  SELECT * FROM `tbl_backup` AS bkup
  WHERE ROW(bkup.col1, bkup.col2) NOT IN
    (SELECT orig.col1, orig.col2 FROM `tbl_target` AS orig);

Monday, April 11, 2011

Replace local home directory with an existing partition

Find the UUID of the partition:
$ blkid /dev/sda1
... or ...
$ ls -l /dev/disk/by-uuid

Edit /etc/fstab file:
UUID=xxxxxxxxx /home ext3 defaults,noexec,nosuid 1 2

Move home to old-home, then remount partition.
$ mv /home /old-home
$ mkdir /home
$ mount -o remount /home

Friday, March 25, 2011

Find and delete large files

Find files larger than 1GB (display filesize and lsat modified time):

$ find <directory> -type f -size +1G
$ find <directory> -type f -size +1G -exec du -h --time {} \;

Sorted by file size (human readable size):

$ find <directory> -type f -size +1G -exec du --time {} \; | sort -n
$ find <directory> -type f -size +1G -exec du -h --time {} \; | sort -h

Find files that are larger than 1GB and older than 5 days (sorted by time):

$ find <directory> -type f -size +1G -mtime +5
$ find <directory> -type f -size +1G -mtime +5 -exec ls -lht {} +;

Find and delete files older than 5 days and larger than 1GB:

$ find <directory> -type f -size +1G -mtime +5 -exec rm {} \;

Friday, February 11, 2011

How to find out CentOS's version

$ cat /etc/issue
CentOS release 5.7 (Final)
Kernel \r on an \m

$ cat /etc/centos-release
CentOS release 6.3 (Final)

$ uname -a
Linux cle-dev 2.6.18-274.18.1.el5 #1 SMP Thu Feb 9 12:45:44 EST 2012 x86_64 x86_64 x86_64 GNU/Linux

$ rpm -qa | grep ^centos

$ yum list installed |grep ^centos
centos-release.x86_64 6-3.el6.centos.9  @anaconda-CentOS-201207061011.x86_64/6.3

# Find out what package were installed with 'yum'
$ yum list installed

# e.g. mysql-server
$ yum list installed |grep ^mysql-server
mysql-server.x86_64   5.1.61-4.el6      @base

# e.g. php modules
$ yum list installed |grep ^php
php.x86_64            5.3.3-14.el6_3    @updates
php-cli.x86_64        5.3.3-14.el6_3    @updates
php-common.x86_64     5.3.3-14.el6_3    @updates
php-gd.x86_64         5.3.3-14.el6_3    @updates
php-intl.x86_64       5.3.3-14.el6_3    @updates
php-mbstring.x86_64   5.3.3-14.el6_3    @updates
php-mysql.x86_64      5.3.3-14.el6_3    @updates
php-pdo.x86_64        5.3.3-14.el6_3    @updates
php-soap.x86_64       5.3.3-14.el6_3    @updates
php-xml.x86_64        5.3.3-14.el6_3    @updates
php-xmlrpc.x86_64     5.3.3-14.el6_3    @updates