Just a few I remember. This is not a full list but you should get idea. Following all are very basic question. I've short answer, for details read man page or use google.
What is the default Window system / Windows manager used in Linux?
What command is used to list the contents of directory?
What command is used to list the top 10 files / directories size wise?
What command is used to display a list of currently running processes?
for X in $(du -s * | sort -nr | cut -f 2); do du -hs $X ; done
What is a login shell?
/proc file system
A program get executed when a user logs into UNIX box. E.g. bash, sh, ksh, csh
What is UID?
User identification number which is assigned to each UNIX / Linux user; it may or may not be unique (unique number is recommended to avoid security related issues). UID and user relationship defined in /etc/passswd file.
What GID? What is EUID? What SUID? What is RUID?
Linux > More on USER ID, Password, and Group management
Understanding /etc/passwd file format
Understanding /etc/ shadow file
Explain Unix User security concept
Permissions - chmod and chown
User groups - group management - user management
Read su, sudo man page
Process identification number; use ps command to see PID. It is a number used by Unix kernels and Windows operating systems to identify a process.
Explain process ID zero and process ID 1?
All the idle task has process ID zero, and never exits.
The init process, with process ID 1, which does nothing but wait around for its child processes to die. Usually started for /etc/inittab
Explain wheel group usage along with an example?
What command is used to check a file system for errors?
Is Linux / UNIX file system case sensitive? Give one example
Yes, test.txt and TEST.txt are two different files
What file contains the list of drives that are mounted at boot?
/etc/fstab - Linux / Other UNIX version
/etc/vfstab - Solaris UNIX
Explain the usage of the fourth field in /etc/fstab?
It is formatted as a comma separated list of options. Read mount command man page for all the option.
What is /etc/inittab file? In what file is the default run level defined?
System V init examines the '/etc/inittab' file for an 'initdefault' entry, which tells init whether there is a default runlevel. init is the program on Unix that spawns all other processes. It runs as a daemon and typically has PID 1.
Common runlevle values on RHEL
To check the current runlevel:
1. Single user mode
3. Default text
5. Default GUI
What command is used to get help about command? What command is used to read manual page for a given command?
What command form or symbol used to redirect output to a file?
Use the > symbol
Use the < symbol to read input from a file
command-name > output.txt
What is ssh? Specify ssh command syntax to execute command over a TCP/IP network?
SSH is Application layer protocol which allows data to be exchanged over a secure channel between two computers.
Sshh - Wikipedia, the free encyclopedia
Explain steps for password less login? How do you set-up SSH with DSA / RSA public key authentication?
ssh firstname.lastname@example.org command-name
Howto Linux / UNIX setup SSH with DSA public key authentication (password less login)
Explain BSD-style init?
Read rc man page. There are no runlevels; the 'rc' file determines how init is to be run.
Runlevel - Wikipedia, the free encyclopedia
Explain Sys-V style init?
Read init man page
Runlevel - Wikipedia, the free encyclopedia
Explain Unix philosophy
Unix philosophy description by The Linux Information Project (LINFO)
What is POSIX? Name 2 POSIX-oriented operating systems?
Portable Operating System Interface is the collective name of a family of related standards specified by the IEEE to define the application programming interface (API). HP-UX, Solaris, AIX etc
Linux and BSD not certified as POSIX but conform to standard.
Explain Raw device and command s to configure Raw device
Block device file that allows accessing a storage device such as a hard drive directly. For example /dev/hda. Use commands
Explain File descriptor
File descriptor - Wikipedia, the free encyclopedia
Explain Unix file types
Explain inode, superblock and hard links
Understanding UNIX / Linux file system
Explain Unix domain socket
MySQL and many programs uses domain socket to make client / server communication. Usually fast as compare to TCP/IP
Explain UNIX software pipeline concept
See shell or bash man page
Explain XYZ Unix daemons
cat /etc/passwd | grep username
mount | grep cdrom
Where XYZ can be any one of the following:
Explain udev in Kernel 2.6?
udev - Wikipedia, the free encyclopedia
Explain Process management and related commands
Explain Memory management and related commands
What is Open Group standards?
Secify seciaal usage for each one of the following file
/dev/null - Send unwanted output
/dev/random - Random number generation
/dev/zero - Cache or Destroy data on a partition - dd if=/dev/zero of=/dev/sda98
Explain Linux Exec Shield