Linux Interview Question

I know for a beginner how tough to find which types of question an interviewer will ask to ?? ...
 
These are the some Question for Reference... 
 
1.     Diff between RHEL 4 & 5 & 6
2.     About boot proces
3.     Types of DNS?
4.     how dns works?
5.     what is squid?
6.     port number of data ftp, ftp, telnet, smtp, sql
7.     what is sendmail hows it's works
8.     How to block downloading in squid
9.     How you handle Load on server?
10. Fields in crontab?
11. Any backup tools you know?
12. How to update your server?
13. rpm commands to update, erase, install etc...
14. Use squid to do authentication of users on browser?
15. Use of NFS and samba?
16. Diff NfS & Samba?
17. What is SeLinux?
18. Default cache size in Squid?
19. I want to assign NISdomainname via DHCP is it possible how?
20. How to setup networking IP doaminname etc...
21. What is & Difference between find and grep
22. About Raid tool used & level diff
23. I want to do remote login how?
24. Use of NIS?
25. Use of Log files?
26.Size of MBR, fields in MBR, PT size in MBR  Dir /abcd have 744 perm to user but file /abcd/file1 has 777 permission can a normal
27. user edit file1, if no why?
28. What happen if a deleted /boot/lilo.conf and restarted the system and
29. What if deleted /boot/grub/grub.conf and restart the system ???
30. what called #! /bin/bash
31. There a parameter in vsftpd conf file without which vsftpd server will not work
32. Diff GRUP & LILO techinical DIFF ...
33. Can we authenticate only users login on vsftpd by LDAP how
34. Port number SAMBA, DHCPD, SQUID, DNS, POP, POP, NTP on secure level, IMAP on secure level,  sendmail on secure level, Postfix..
35. Diff TCP/UDP
36. What are 7 Layers TCP/IP eg of each
37. Fields in DNS
38. USe of ip_farwording
39. where is config file of sshd service.
40. what is tunnel
41. What is mutt
42. fields in top command meanings
43. What is the use of swap partition
44. can we encrease swap partition size how
45. syntax of for loop in bash
46. awk stand for
47. can we change vsftpd default directory location
48. Can we change Default Directory in apache
49. Can we use index.php insted of index.html as default page in apache how .
50. visudo command will open file?
51. Diff RHEL & CentOS & Fedora
52. Diff LILO GRUB
53. Advantages of GRUB
54. What is iptables, Firewall, netfilter ..?
55. How to block the specific port.
56.

 Tables in iptables

57. what is cluster & virtualizaton just basic, what you understand by term..
58. what is domain and hostname concept.
59. can a system have multiple hostname/domainname how?
60. How many virtual ips you can assign to a single interface.
61. What is netmask/ broadcast IP ?
62. What is inode in Linux
63. What is Raid5, advantage of Raid5 over Raid4 over Raid1 over Raid0
64. Can we safely delete /usr/shares  Impacts ?
65. Use of loge levels ?
66. What is suid, guid and sticky bit
67. Can you open multiple vi on same terminal at a time
68. What is sed command, any advantage
69. Use of KILL and KILL command
70. Use KILL command to reload a service eg: HTTPD
71. What s vlan
72. How to find number of users on your system
73. Find port use by a process
74. Find file's opened by a process
75. what is fork and prefork
76. What is sticky bit, suid, guid, when to use which
77. Ramdisk when and how to use?
78. Diff Samba and NFS
79. What is tcpdump, when and how to use.
80. print whole file other than cat
81. What is hub, switch and router
82. What is segmentation fault
83. What is diff between Single user mode and Emergency mode
84. How to downgrade an rpm .
85. How to rebuild rpm db
86. List files in rpm
87. reinitialize file permission of an installed rpm
88. Active and Passive FTP
89. What is getopts how it's work
91. Diff Shell Login and Intractive Login

91. DNS,
92. What is SOA,A, PTR,Cname,NS record
93. What is MX record
94. nslookup, check which entry first
95. use of nsswitch.conf
Njoy...
 

Linux Crontab

Linux Cron utility is an effective way to schedule a routine background job at a specific time and/or day on an on-going basis.


 Linux Crontab Format

MIN HOUR DOM MON DOW CMD

Table: Crontab Fields and Allowed Ranges (Linux Crontab Syntax)

Field	Description	Allowed Value
MIN	Minute field	0 to 59
HOUR	Hour field	0 to 23
DOM	Day of Month	1-31
MON	Month field	1-12
DOW	Day Of Week	0-6
CMD	Command	Any command to be executed.

Scheduling a Job For a Specific Time Every Day

The basic usage of cron is to execute a job in a specific time as shown below. This will execute the Full backup shell script (full-backup) on 10th June 08:30 AM.

Please note that the time field uses 24 hours format. So, for 8 AM use 8, and for 8 PM use 20.

30 08 10 06 * /home/Sadeek/full-backup

• 30 – 30th Minute
• 08 – 08 AM
• 10 – 10th Day
• 06 – 6th Month (June)
• * – Every day of the week

Schedule a Job For More Than One Instance (Twice a Day)

The following script take a incremental backup twice a day every day.

This example executes the specified incremental backup shell script (incremental-backup) at 11:00 and 16:00 on every day. The comma separated value in a field specifies that the command needs to be executed in all the mentioned time.

00 11,16 * * * /home/sadeek/bin/incremental-backup

• 00 – 0th Minute (Top of the hour)
• 11,16 – 11 AM and 4 PM
• * – Every day
• * – Every month
• * – Every day of the week

Schedule a Job for Specific Range of Time (Only on Weekdays)

If you wanted a job to be scheduled for every hour with in a specific range of time then use the following.

Cron Job everyday during working hours

This example checks the status of the database everyday (including weekends) during the working hours 9 a.m – 6 p.m

00 09-18 * * * /home/sadeek/bin/check-db-status

• 00 – 0th Minute (Top of the hour)
• 09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
• * – Every day
• * – Every month
• * – Every day of the week

How to View Crontab Entries ?

 sadeek@localhost$ crontab -l 

@yearly /home/sadeek/annual-maintenance 

*/10 * * * * /home/sadeek/check-disk-space

  [Note: This displays crontab of the current logged in user]

View Root Crontab entries

 root@localhost# crontab -l
no crontab for root

Crontab HowTo View Other Linux User’s Crontabs entries

To view crontab entries of other Linux users, login to root and use -u {username} -l as shown below.
root@localhost# crontab -u sadeek -l
@monthly /home/sadeek/monthly-backup
00 09-18 * * * /home/sadeek/check-db-status

Edit Root Crontab entries

Login as root user (su – root) and do crontab -e as shown below.

root@localhost# crontab -e

Edit Other Linux User’s Crontab File entries

To edit crontab entries of other Linux users, login to root and use -u {username} -e as shown below.

root@localhost# crontab -u sadeek -e
@monthly /home/sadeek/fedora/bin/monthly-backup
00 09-18 * * * /home/sadeek/centos/bin/check-db-status
~
~
~
"/tmp/crontab.XXXXyjWkHw" 2L, 83C