Q : What is the difference between service and process?
A process is any piece of
software that is running on a computer. For example, your anti-virus software
runs in the background as a process, which was automatically started when the
computer booted. Some processes start when your computer boots, others are
started manually when needed.
Some processes are services that
publish methods to access them, so other programs can call them as needed.
Printing services would be an example of a service type of process, where your
email program can just call the print services process to say it wants to
print, and the service does the actual work.
Q : How to view
crond status? If it’s show service is not found.
Service crond
restart
Q. How to FTP
user access other directory except his own home directory?
vim /etc/vsftpd/vsftpd.conf
Chroot_list_enable=yes
Q. What are the
Linux-based security tools?
Selinux
Firewall
iptables
Tcp-wrappers
Q. What are the
basic elements of firewall?
A firewall
should be able to filter packets (drop/pass them) based on certain rules
specified by the user. The rules may be used to identify an incoming packet to
the computer or outgoing packet from the computer, it can be based on target
port number/ip add , traffic from a particular Network card etc…
The firewall
rules can be in a tabular form (saved on the disk) from where the firewall
software can read them and implement it. iptables firewall on Linux is a great
example
Q. What is a
command to display top 10 users who are using huge space?
du -sh /home/* | sort -r | head -10
Q. How do find
all failed login attempts via ssh?
tail -f /var/log/secure | grep Failed
Q. How do you
configure Linux system as a router?
vim /etc/sysctl.conf
net.ipv4.ip_forward=1
system-config-network
eth0 192.168.1.120 eth0:1 172.24.0.1
255.255.255.0 255.255.0.0
172.24.0.1 192.168.1.120
Q. What is the
UID and GID of root user? Can a normal user can change the ownership of a file?
What is the command to change ownership of a file?
The root UID/GID
is 0 (zero). Which is why he can able to intervene in all normal users files
even though he don’t had permission. A normal user will don’t have the
permission to change ownership of file. The command to change ownership is <
chown user.user file >
Q. What is the diff b/w ext2 and ext3?
Ext3 is a tiny
bit slower than ext2 is, but it holds tremendous advantages. There is really
only one difference between ext2 and ext3, and that is that ext3 uses a journal
to prevent filesystem corruption in the case of an unclean shutdown (ie. before
the filesystem is synced to disk). That makes ext3 a bit slower than ext2 since
all metadata changes are written to the journal, and then flushed to disk, but
on the other hand you don’t risk having the entire filesystem destroyed at power
failure or if an unwitted person turns the computer off uncleanly. You don’t
have to check the filesystem after an unclean shutdown either. Ext3 has three
levels of journalling. Metadata (ie. internal filesystem structures) are always
journalled, so that the filesystem itself is never corrupted. How ordinary data
is written to the file system is controllable, though. The default option is
the “ordered” mode, which causes file contents to be written to the filesystem
before metadata is even committed to the journal. The highest reliable mode is
called the “journal” mode, which causes file data to be committed to the
journal before it is flushed to its final place, like the metadata. The least
reliable mode, but rumoured to be the fastest, is called the “writeback” mode,
which makes no promises at all regarding the consistency of file data. Only
metadata is output reliably in writeback mode. So as for anything else, it’s
mainly a matter of priority. If you don’t want ultimate speed, go with ext3. If
you need the highest speed that is theoratically aquirable though, then go with
ext2. For that to be effective you’ll probably need a really advanced hard
drive controller, though.
Q. As the
system administrator you need to review Bob’s cronjobs. What command would you
use?
crontab –lu Bob
Q. What command
is used to remove the password assigned to a group?
gpasswd –r groupname
Q. What are the different RAID levels?
RAID level 0
RAID level 1
RAID level 2
RAID level 3
RAID level 4
RAID level 5
RAID level 6
RAID level 10
RAID level 50
Q. How do you
create a swapfile?
dd if=/dev/zero of=/swapfile bs=1024 count=200M
mkswap /swapfile
swapon /swapfile
Q. What does
nslookup do?
Nslookup is a program used to find information about
internet Domain Name server.
The two modes of nslookup are: Interactive and
non-interactive.
Using ‘interactive mode’ user can query the name
servers for the information pertaining to hosts and domains.
Using ‘non-interactive mode’ the user can just print
the name and requested information of a host.
Q. What is the
difference between UDP and TCP?
TCP is a Transmission Control Protocol.
UDP is a User Datagram Protocol.
There are four major differences between UDP and TCP:
1. TCP can establish a Connection and UDP cannot.
2. TCP provides a stream of unlimited length, UDP
sends Small packets.
3.TCP gurantees that as long as you have a connection
data sent will arrive at the destination, UDP provides not guarantee delivery.
4.UDP is faster for sending small amounts of data
since no connection setup is required, the data can be sent in less time then
it takes for TCP to establish a connection.
Q. What command
do you run to check file system consistency?
Need to run fsck [file system consistency check]
command to check file system consistency and repair a Linux / UNIX file system.
Fsck
Q. What is the
command to remove Lvm ,Pv and vg
1st remove the entry on /etc/fstab file & save –
quit.
2nd remove LVM – lvremove lvname
3rd remove VG – vgremove vgname
4th remove PV – pvremove pvname
Q. How to
create SAMBA server in fedora 9 Linux?
yum install samba -y
yum install samba-swat –y
vi /etc/samba/smb.conf
comment = windows sharing
path = path/your/share/directory
valid users = surendra
writable = yes
browseable = yes
then type testparm for code testing.
smbpasswd -a username
smbpasswd -e username
service smb restart
chkconfig smb on
Q. How to
schedule cron backup to run on 4th Saturday of month?
* * * * 6 weekdaynum 4 && sh /backup/test.sh
Q. What is an
inode?
ext2 and ext3 file systems keep a list of the files
they contain in a table called an inode table. The inode is referenced by its
number. This is unique within a file system.
The inode contains the metadata about files. Among the
data stored in the inode is
File type
File permissions
Link count
User ID number of the file owner and the group ID
number of the associated group
Last modification time
Location of the data on the hard disk
Other metadata about the file
ls -li – view inode number only
stat /etc/passwd – view inode details
Q. How to see
unallocated hard disk space on linux
df -h
Q. How do u
find remote machine operating system and version?
nmap -A –v 192.168.1.100
Q. How do you
port scanning with netstat command?
netstat –an
Q. Linux system
monitoring Tools?
top – Process Activity Command
vmstat – System Activity, Hardware and System
Information
w – Find out Who Is Logged on And What They Are Doing
Uptime – Tell How Long the System Has Been Running
ps – Displays the Processes
free – Memory Usage
iostat – Average CPU Load, Disk Activity
sar – Collect and Report System Activity
mpstat – Multiprocessor Usage
pmap – Process Memory Usage
Q. Linux
Network monitoring Tools?
netstat and ss – Network Statistics
iptraf – Real-time Network Statistics
tcpdump – Detailed Network Traffic Analysis
strace – System Calls
/Proc file system – Various Kernel Statistics
# cat /proc/cpuinfo
# cat /proc/meminfo
# cat /proc/zoneinfo
# cat /proc/mounts
Nagios – Server And Network Monitoring
Cacti – Web-based Monitoring Tool
Gnome System Monitor – Real-time Systems Reporting and
Graphing
Q. What is mean
by system calls?
A system call is the mechanism used by an application
program to request service from the operating system.
On Unix-based and POSIX-based systems, popular system
calls are open, read, write, close, wait, exec, fork, exit, and kill. Many of
today’s operating systems have hundreds of system calls. For example, Linux has
319 different system calls. FreeBSD has about the same (almost 330). Tools such
as strace and truss report the system calls made by a running process.
Q. How do u
extract files from iso cd images in linux?
mount –o loop disk1.iso /mnt/iso
Q.
What
is Clustering?
Clustering
means it is a group of two or more server running same application and fault
tolerance it is called Clustering.
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