Apache, cron and proxy

Gaurav Mishra
<gmishx@gmail.com>
Linux - 5
Apache Configuration file,
Cron jobs,
Proxy server
2/27/2018
Unrestricted

Gaurav Mishra <gmishx@gmail.com>
Apache http server
• One of the most commonly used open source sever
• Can be easily tuned
• Works in harmony with PHP
• Provides various security measures
• Installs as httpd in many Linux distros
• Packages as apache2 in Debian based distributions
2/27/2018

Apache directory structure
• The apache foundation have their hierarchical structure for the respective
configuration files.
• The root is located at: /etc/apache2/
• The main configuration file is located at ./apache2.conf
• The modules currently installed are located at: ./mods-available/
• The modules currently in use are located at: ./mods-enabled/
• The websites/virtual host available for current install are located at: ./sites-available/
• The websites/virtual host being used for current run are located at: ./sites-enabled/
2/27/2018

Apache configuration file
• The global configuration file is stored at /etc/apache2/apache2.conf
• Can be overridden for each directory using .htaccess
• The file contains directives, mostly distributed in directive blocks
• Commonly used directive blocks:
▫ directory
 Contains directives defined for a particular directory
▫ VirtualHost
 Directives defined for a virtual host
2/27/2018

List of common directives
• Alias
• Allow
• AllowOverride
• AuthBasicAuthoritative
• AuthType
• Deny
• <Directory>
• DocumentRoot
• <Else>
• ErrorLog
• ErrorLogFormat
• <If>
• <IfModule>
• Include
• KeepAlive
• Listen
• LoadModule
• Redirect
• RedirectMatch
• ServerAdmin
• ServerAlias
• ServerLimit
• ServerName
• SSLCertificateFile
• SSLCertificateKeyFile
• SSLEngine
• <VirtualHost>
2/27/2018

Setting up directory directive
Alias “/holidaypics” “/var/www/html/newpics”
<Directory /var/www/html/newpics>
AuthType Basic
AuthName Newpics
AuthUserFile /web/users
AuthGroupFile /web/groups
<IfModule mod_dir.c>
DirectoryIndex index.php
</IfModule>
<Files dinner.jpg>
order deny,allow
deny from all
allow from 127.0.0.1
</Files>
</Directory>
2/27/2018

Setting up VirtualHost
• Virtual hosting allows the Apache web server to host multiple websites as part of its
own.
ServerName server.example.com
ServerAlias server server2.example.com server2
ServerAlias *.example.com
<VirtualHost server.example.com:80>
Alias /files /home/user/Documents/files
<Directory "/home/user/Documents/files">
AllowOverride None
Options FollowSymLinks MultiViews
</Directory>
</VirtualHost>
2/27/2018

Setting up SSL support
<IfModule mod_ssl.c>
<VirtualHost *:443>
SSLEngine on
SSLCertificateFile /etc/ssl/certs/certi.cer
SSLCertificateKeyFile /etc/ssl/keys/certi.key
</VirtualHost>
</IfModule>
2/27/2018

Apache tools
• To enable a website configuration from /etc/apache2/sites-available/mysite.conf
▫ a2ensite mysite
• To disable a website configuration from /etc/apache2/sites-available/mysite.conf
▫ a2dissite mysite
• To enable a module from /etc/apache2/mods-available/mymod.conf
▫ a2enmod mymod
• To disable a module from /etc/apache2/mods-available/mymod.conf
▫ a2dismod mymod
• Check the syntax of apache2.conf
▫ apachectl configtest
2/27/2018

Cron jobs
• Cron jobs are set of actions which must be executed at a certain time on a given day.
• Cron daemon keeps checking these cron jobs and execute them whenever required.
• Each user can have their own cron jobs.
• The job set by a user run with their privileges.
• The cron jobs are stored in crontab files.
2/27/2018

Crontab format
• The format of a crontab field follows:
▫ minute hour day-month month day(s)-week task
• A crontab entry has six fields:
▫ The first five are used to specify the time for an action
 The first field specifies the minute (0–59)
 The second field specifies the houst (0-23)
 The third field specifies the day of the month (1–31)
 The fourth field specifies the month of the year (1–12, or month prefixes like Jan and Sep)
 And the fifth field specifies the day of the week (0–6, or day prefixes like Wed and Fri),
starting with 0 as Sunday.
▫ The last field is the action itself.
• Each field can be defined as range or using * to match all
2/27/2018

Crontab examples
• Take backup at 2:00 AM from Mon-Friday of every month
▫ 0 2 * * 1-5 tar cf /home/backp /home/projects
• Take backup at 2:00 AM on Sun, Wed, Fri of every month
▫ 0 2 * * 0,3,5 tar cf /home/backp /home/projects
• Take backup every other day at 2:00 AM on any day
▫ 0 2 */2 * * tar cf /home/backp /home/projects
2/27/2018

Adding a cron job
To add a cron job
1. First write the job in the respective 6 columns in a file.
▫ echo “0 2 * * 1-5 tar cf /home/backp /home/projects” > mybackup_script
2. Pass the file to crontab
▫ crontab mybackup_script
To edit a job already added
1. Open the crontab in edit mode
▫ crontab -e
2. Edit the job
3. Save the changes
Check all the jobs for current user
• crontab -l
2/27/2018

Cron file organization
2/27/2018

Proxy servers
• Proxy servers acts as an intermediate
between the client and the server.
• They serve many purpose.
• Caching
• Anonymizing
• Load management
• Redirection
• Every client sends a request to the
proxy, the proxy checks if it can serve
the request from it’s cache otherwise
forward it.
• Proxy sometimes helps working with
firewalls.
2/27/2018

Setting up proxy on host
• Majority of the software support proxy
• The most common place to find the proxy setting is in the System environment
variable http_proxy, https_proxy, ftp_proxy.
• The variables can be set using the export command a given terminal session.
• They can also be set using the /etc/profile and /etc/bash.bashrc files for sessions
globally.
• The string follows following pattern:
▫ [username]:[password]@ipaddress:port
▫ http://[username]:[password]@address.com:port
2/27/2018

Apache, cron and proxy

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