Answer:

To check which Apache modules are loaded, in RHEL/Fedora/CentOS, type

# httpd -M

In Debian/Ubuntu

# sudo apache2ctl -M

Answer:

If you are running in Red Hat Linux/ Fedora/ CentOS

# httpd -V
....
Architecture:   64-bit
Server MPM:     Prefork
  threaded:     no
    forked:     yes (variable process count)
...

If you are running in Debian/ Ubuntu, you can use apache2 -V, which get the same output as above.

Answer:

If you want to sync the system time without installing ntpd package, rdate is an older way but it will do what you need.

# rdate -s ntp0.cornell.edu

You can find a list of time servers at: http://pank.org/blog/2004/08/time-server-list.html

Answer:

You can use the following command to remove packages using yum,

e.g. remove Firefox

yum remove firefox

To remove multiple packages, try

yum remove firefox gedit

Answer:

To remove installed package using rpm, use the following command

e.g. remove Firefox

rpm -e firefox

To remove multiple packages, try

rpm -e firefox gedit

Answer:

Sometimes, if you forgot to select "Development Tools" during Fedora/CentOS installations, you can add them later by using one command

yum groupinstall "Development Tools"

Which save you a lot of times from installing the needed packages one by one.

To see what options are available for groupinstall, try

yum grouplist

Answer:

Assume you have foo.rpm, type the following command to extract the rpm's contents

rpm2cpio foo.rpm | cpio -idmv

Answer:

iptables -A INPUT -s IP -j DROP


Replace IP with the actual remote IP address.

Note that the blocking will be lost when server reboot. You would need to save the rule(s) into a script and reload when server reboot.

Answer: (pick either one)

1. Change the run-time configuration (won't take effect when you reboot)

# sestatus informs you of the two permission mode statuses,
# the current mode in runtime and the mode from the config
# file referenced during boot:

setenforce 1
sestatus | grep -i mode
Current mode: permissive
Mode from config file: enforcing


2. Turn off SELinux permanently, use the following command

system-config-securitylevel


Source: http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/selinux-guide/rhlcommon-section-0068.html

Answer:

To query if a package is installed, e.g.

rpm -q httpd


To display package information, e.g.

rpm -qi httpd