How to check installed packages?

For example to check whether you have firefox installed you can use rpm utility available on RedHat enterprise Linux :
[root@ice ~]# rpm -qa |grep firefox firefox-1.0.7-1.4.3
 

How to enable telnet services on Redhat enterprise Linux?

# chkconfig telnet --list #chkconfig telnet on #chkconfig --level 35 telnet on

where 3 and 5 are run levels , so telnet will run when Linux is running in runlevel 3 and 5 only.
 

How to change Redhat Linux system default run level?

1. edit /etc/inittab file and changerun level from level 5 (which is X or GUI mode ) to run level 3

# vi /etc/inittab id:3:initdefault:

2. simply reboot the server and your default run level changes to level 3 which is text based linux session.

3. How to dynamically change the runlevel of Linux system without rebooting

- e.g: switch to single user mode : 

# telinit  S 

- e.g: switch to X or GUI (desktop) mode 

#telinit  5 

- e.g: If you have made changes to the /etc/inittab file to change the default runlevel and want to change the system to that new default you can do so by using the telinit with the q command-line option: 

# telinit  q 
 

For RHCE and RHCT exam you should know RHEL4 boot sequence as follows:

• Bios Initialization 
• Loading Boot Loader phase 
• Kernel initialization 
• init startup which is first process to run in Linux during startup 
• Launching X or GUI if enabled 

• Click Ctrl+N or select create new Virtual machine from File menu Select Typical in Vmware Wizard 
• Under new machine virtual wizard select LINUX as guest operating system and version as redhat enterprise Linux 4 or 1,2,3. 

 
• For Fedora select other as an option in VMWARE wizard: 
• You can choose location for to save configuration for virtual location , I used my documents: 

 
• Select "use bridged networking" in VMWARE wizard to provide guest os direct access to an external network: 

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