Linux:GUI troubleshooting


Linux server's can be accessed through GUI(Graphical User Interface) or CLI(Command Line Interface).

Some times User will face some issues when accessing GUI such as

  • Blurred screen.
  • System crashes when users try to access GUI.
  • Only particular user will face an issue not able to access GUI.
  • Resolution problems.
In order to resolve this issues we have to pin point the problem, check weather its a problem with the single user or all the users in the server not able to access the GUI

ISSUE1: If it is for a single user this GUI related problems will occur due to some space issue
So check these following things
  1. Check weather his disk quota is exceeded or not(when ever GUI is started in Linux/Nix it require some temporary space which is used to store some temp files for the purpose of GUI running), so if there is no free space left for the user GUI will not start for that particular user.
  2. Remove temporary files which are not in use for that particular user.

ISSUE2: If the GUI is not working for all the users then there is some configuration issues in xorg.conf file.

The best and simple way to resolve this issue is just take a backup of the existing file and regenerate the new config file

#mv /etc/X11/xorg.conf /etc/X11/xorg.conf.old

Regenerating new GUI configuration file


this command will regenerate fresh GUI and it will ask you for new resolution too, so set the new resolution to your requirement.

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  • DNS Troubleshooting in Linux


    Some basic DNS troubleshooting in Linux.
    1. First collect the information which has created the problem by doing some investigation(such as logs, debug messages etc) .
    2. Prepare your tools which is required for your troubleshooting.
    3. Troubleshooting is nothing but considering so many issues that may cause the problem and working one by one to pin point the actual culprit which created the issue.
    4. once issue is pin-pointed you have to work on that issue with the tools/commands/logs all other resources and have to resolve it.

    Coming to troubleshooting DNS aka named services, here are the steps how we can resolve the DNS related issue:

    I will take one scenario "suppose my client is unable to resolve host-names to IP address"

    Step1:Check the DNS server is configured on Client end or not

    check in below file if name server is configured to proper DNS server or not
    #vi /etc/resolv.conf

    If the client is configured with proper DNS server follow to next step

    Stpe2:Ping to DNS server ip address

    #ping serveripadd

    If pinging is happening proceed with the next step other wise click here to do network troubleshooting.

    Step3:So pinging is happening... then there is a communication path between Server-client, so we have to check weather DNS server is running or not. Here nmap can be used to check what ports opened on server.

    #nmap serveripadd



    this command will give you output what are the services running/ports opened on remote server, if DNS server is running and working fine means you can see DNS port(53) in the list of opened ports. If suppose server is not running/port blocked you can click here to troubleshoot in this way.

    Step4:Now checking DNS server issue in deep

    • Checking under whom the DNS server is register and its properties .

    • Checking what server is used to resolve and some basic info.

    • Checking who is resolving and what is resolving in details about DNS server.

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  • Disabling SELinux


    Some basics of SELinux :
    How to disable SElinux?
    SElinux is a security feature which was shipped with RHEL5, it is much secure than any other security priviously such as PAM and Initd

    Here we are going to see some basics of SElinux.

    Step1:Seeing whether SELinux is enabled or not ?


    Step2:To see SELinux status in elaborated way you can use sestatus
    SElinux status : enabled
    SELinux mount : /selinux
    Current mode : enforcing
    Mode from config file : enforcing
    Policy version : 21
    Policy from config file : targeted

    From the above output we can see that SElinux is enabled and its in enforced mode.
    and to see detailed status you can use -b option, this will give which service are SElinux enabled and which services are disabled.

    /etc/grub.conf and /etc/selinux/config

    Step3:disabling SElinux
    We can do it in two ways
    1)Perminant way : edit /etc/selinux/config

    change the status from enable to disable and selinux type from strict to targeted, after changes are made we have to restart, if the server's are in production and don't want to restart the server follow the temporary way of disabling it.

    2)Temporary way : echo 0 > /selinux/enforceFor your info if you want to enable it again, try below commandecho 1 > /selinux/enforce.
    Selinux is a vast subject and can not deal in one post, see for my other posts regarding Selinux.

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  • Recovering Ubuntu Grub bootloader


    I was having trouble with Windows and I installed Ubuntu on my laptop. Unfortunately I re-installed windows after Ubuntu and now I don't have the option of viewing the boot menu to select Ubuntu. I was using the dual boot mode. Is there a way to view the boot menu in Windows XP that will allow me to select Unbuntu again?

    This is some what tricky question, acutually when you install Ubuntu the bootloader "GRUB" will take care of MBR(Master boot record) and boot menu details such as OS's present either its a linux/nix or windows, because GRUB is a universal bootloader which will understand most of the OS's. But it is not the case with Windows bootloader boot.ini which cant not understand other then Windows,

    So when you reinstall windows after Ubuntu, the Windows OS will rewrite the MBR and bootmenu with its own parameters. So your system doesnot know where Ubuntu/linux is located

    To resolve this issue just use Ubuntu live cd and reinstall GRUB boot loader.

    If you are using Redhat and windows follow below procedure
    Step1 : Insert the first cd of your linux and boot from cd.

    Step2 : Start with linux rescue method.

    Step3 : Mount the partitions via chroot.

    then install grub through

    #grub-install /dev/hdc

    Step4 : reboot
    now u will get GRUB loader and your Linux will be rescued.

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  • Login Problems


    Login Problems

    When a user/root try to login to Linux system there are so many problems which will prevent the root/user not to login.

    Here we will see what are the problems which will prevent user from not to login to system and try to resolve them one by one.

    We can divide these problems in to two categories:
    1. Physically present at system.
    2. Accessing system from remote location(through network).

    Logging in to the system when you are present infront of the system.

    Issue1:Check weather the password you are typing is correct or not, what I mean is Case sensitive etc,
    here I am considering that you forgot the password for that system, In this case follow these steps

    Issue2:Still not able to login to system except runlevel1, so how to resolve this issue?
    • Check root user properties such as shell type, age and security etc?

    Step1 : Check the root properties by using finger command.

    #finger root
    Login: root Name: root
    Directory: /root Shell: /sbin/nologin
    Never logged in.

    this command will give you the properties of the root user, here we have to check what is the shell he is using, the shell should not be nologin shell. If the shell for the root user is no login shell he will not able to login to system so we have to change the login shell from /sbin/nologin shell to some other shells such as /bin/bash.
    To do this we can use chsh command

    #chsh -l

    This command will display all the shell's installed in your system, to change the shell.

    #chsh /bin/bash

    then execute finger command to check weather shell has been changed to our required shell or not

    #finger root

    Step2 : Still not able to login? try if there is any age related issues is there on root user

    #chage -l root

    It will display the age related info for the root user.
    Please increase the age of the root user expiry time

    #chage root

    Step3 : Still unable to login? Check for security related restriction on root user

    Check in /etc/securetty file wether all the entries are there or not(in this file there will be entirs of the terminals from where root user can access the system) check weather tty1 to tty7 and vc1 to vc7 are there or not if they are not there add them and try to login.

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  • Lost Root password


    Lost the Root password

    When you lost root password how you can recover and login back in to the system?
    To login in to system there are so many ways to get root access depending on security level of the system.
    Method1: When there is no password set to access runlevel 1.

    Here are the steps to change your root password the most esiest way is as follows..

    1. Start your computer when you see Redhat Linux boot loader(GRUB menu where you can see all the Operating system's in the system) select the redhat linux and press "e", and select second line where you can set the temporary runlevel for the system to boot

    2. You will notice that now you can edit boot loader command arguments now again press "e" and edit the line to add single or 1 without quots at the end of line.

    3. Press enter to return to previous screen

    4. Press b to boot with this new argument which will run Linux into single user mode. Please make sure that you see single at the end of line.

    5. Now you will get root login with out asking for a password in single user mode.

    6. Use "passwd" command to change your password.
    here it will not ask previous password so you can just enter new password.

    7. When updateing the password in runlevel1 if the server is not allowing you to change password giving you error, this is due to /etc/shadow file issue.
    In order to resolve this issue execute the following command and then try to change the password


    7.After changing the password just type exit command which will take you to default runlevel of the system or just Reboot and use the new password.

    Method2: When GRUB boot loader is protected with a password.
    When the GRUB boot loader is protected by a password the above mentioned method will not work, so how to login to the system?
    In order to retrive root password we have to have first RHEL cd or a live CD(may be konpics/Ubuntu) .

    It is easy to boot using the first Cd.
    then enter into the rescue mode
    just type linux rescue and boot prompt with out quoat

    Now we will be logged in to a normal shell, do the folowing steps
    Step1 : change the root partation to /mnt/sysimage

    chroot /mnt/sysimage

    Step2 : Now just change the password

    Step3 : Exit from rescue mode

    then login with the new passwd
    And if you don't have the correct version CD, you can boot from a live CD,
    Mkdir /a
    mount ... /a
    vi /a/etc/password

    delete the password in /etc/shadow for root
    Now it will come up with no root password (change immediately).

    Method3: This method will give you how to retrive your lost root password, not for changing the root password
    So how to recover the root password? We can use Rainbow tables technic to do this.

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  • New RHCE Examination pattern


    Recently from 1st May 2009 RHCE(Red Hat Certified Engineer) exam pattern has been changed. Some of the high lights are as follows.. The examination time has been reduced to 3.5 hours from 5.5 hours as it was previously

    1. Previously, there will be two sessions one with 2.5hour(for basic troubleshooting) session and 3hours session(for server and security configurations)
    2. But this time The content has be consolidated and reorganized into a single section.
    3. Every thing will be installed and given along with Visualization, the candidate should complete that exam is one stretch that is 3.5hrs.
    4. As you know RHCE5 SElinux is enabled so prepare along that lines.
    5. Main thing to pass this exam is just practice practice practice
    Get counseling on how to pass RHCE, just fill this form for any quires dont hesitate We will charge for this with minimal amount..

    Study Points for the RHCE Exam

    Prerequisite skills for RHCT and RHCE

    Candidates should possess the following skills, as they may be necessary in order to fulfill requirements of the RHCT and RHCE exams:
    • use standard command line tools (e.g., ls, cp, mv, rm, tail, cat, etc.) to create, remove, view, and investigate files and directories
    • use grep, sed, and awk to process text streams and files
    • use a terminal-based text editor, such as vim or nano, to modify text files
    • use input/output redirection
    • understand basic principles of TCP/IP networking, including IP addresses, netmasks, and gateways for IPv4 and IPv6
    • use su to switch user accounts
    • use passwd to set passwords
    • use tar, gzip, and bzip2
    • configure an email client on Red Hat Enterprise Linux
    • use text and/or graphical browser to access HTTP/HTTPS URLs
    • use lftp to access FTP URLs

    RHCT skills

    Troubleshooting and System Maintenance

    RHCTs should be able to:
    • boot systems into different run levels for troubleshooting and system maintenance
    • diagnose and correct misconfigured networking
    • diagnose and correct hostname resolution problems
    • configure the X Window System and a desktop environment
    • add new partitions, filesystems, and swap to existing systems
    • use standard command-line tools to analyze problems and configure system

    Installation and Configuration

    RHCTs must be able to:
    • perform network OS installation
    • implement a custom partitioning scheme
    • configure printing
    • configure the scheduling of tasks using cron and at
    • attach system to a network directory service, such as NIS or LDAP
    • configure autofs
    • add and manage users, groups, quotas, and File Access Control Lists
    • configure filesystem permissions for collaboration
    • install and update packages using rpm
    • properly update the kernel package
    • configure the system to update/install packages from remote repositories using yum or pup
    • modify the system bootloader
    • implement software RAID at install-time and run-time
    • use /proc/sys and sysctl to modify and set kernel run-time parameters
    • use scripting to automate system maintenance tasks
    • configure NTP for time synchronization with a higher-stratum server

    RHCE skills

    Troubleshooting and System Maintenance

    RHCEs must demonstrate the RHCT skills listed above, and should be able to:
    • use the rescue environment provided by first installation CD
    • diagnose and correct boot failures arising from bootloader, module, and filesystem errors
    • diagnose and correct problems with network services (see Installation and Configuration below for a list of these services)
    • add, remove, and resize logical volumes
    • diagnose and correct networking services problems where SELinux contexts are interfering with proper operation.

    Installation and Configuration

    RHCEs must demonstrate the RHCT-level skills listed above, and they must be capable of configuring the following network services:
    • SMB
    • NFS
    • FTP
    • Web proxy
    • SMTP
    • IMAP, IMAPS, and POP3
    • SSH
    • DNS (caching name server, slave name server)
    • NTP
    For each of these services, RHCEs must be able to:
    • install the packages needed to provide the service
    • configure SELinux to support the service
    • configure the service to start when the system is booted
    • configure the service for basic operation
    • Configure host-based and user-based security for the service
    RHCEs must also be able to:
    • configure hands-free installation using Kickstart
    • implement logical volumes at install-time
    • use iptables to implement packet filtering and/or NAT
    • use PAM to implement user-level restrictions

    Please comment on your experience of RHCE exam

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  • Linux Interview Questions:Google


    Q2) Write a command to find all of the files which have been accessed within the last 30 days.
    A1) The Command is , find / -atime +30
    A2) # find / -type f -mtime +30
    A3) find / -type f -mtime -30
    A4) find / -type f -atime -30 = accessed
    find / -type f -ctime -30 = changed
    find / -type f -ctime -30 = modified
    Q3) How to schedule cron backup to run on 4th saturday of month??
    A1) crontab -e
    ** ** ** ** /5
    Q4) how to see unallocated hard disk space on linux
    A1) simply type
    cat /proc/partitions
    A2) df -h /dev/devicename
    device name could be hda,sda
    Q5) find out what file systems supported by kernel?
    A1) # fdisk /dev/hdx
    option: t
    it will show the supported FS in the kernel
    A2) cat /proc/filesystems
    will show all the file system types that the kernel can
    handle currently. Be aware that kernel will load the
    necessary modules automatically if it have, for a new file
    system type present in a new device you plug into it and
    then the output of the above command will vary.
    A3) you can give following commands
    then press t
    this command will show all the file system with code
    supported by the current linux kernel.
    Q6) how do u extract files from iso cd images in linux?
    A1) From ISO MAGIC
    A2) mount -o loop
    A3) mount -t iso9660 -o ro,loop=/dev/loop0 /home/ste/cd.iso /mnt/iso
    Q7) how do u find remote machine operating system and version?
    A1) XProbe
    A2) by ssh to that machine then give command
    #uname -r
    A3) for OS,
    cat /etc/issue and version, uname –r
    Q8) how do you port scaning with netcat command?
    A1) nc -z
    Q9) how do find all failed login attempts via ssh?
    A1) check network connectivity check correct ipaddress
    ping ipaddress
    A2) 'who' or 'w' is the command used to find the users who logged in
    The system and their attempts, with the help of some options
    A3) Failed ssh logs are either written in /var/log/messages, or
    /var/log/secure (configurable in /etc/syslog.conf). I am
    assuming that the failed login attempts are recorded in
    grep ' authentication failure' /var/log/secure | sed -e
    's/^\(.*\)\(rhost.*\)$/\2/p' | tr -s " " | cut -f2 -d"=" |
    cut -f1 -d" " | sort -n | uniq -c
    Will show you the count, and the IP/hostname of machines that tried
    to access the system via ssh
    A4) The command is ,
    cat /var/log/messages | grep "Failed password"
    it will show all the user which is not able to login.
    Q10) How do display error messages instantly when command fails?
    A1) Suppose you are trying to cat a non existing file:
    cat /etc/shado 2>/dev/null || echo “Failed to open file”
    command 2 "echo" is executed only if command 1 "cat" returns
    a non-zero exit status
    # cat /etc/shado 2>/dev/null || echo "Failed to open file"
    Failed to open file
    Q11) How do find hard disk revolutions speed?
    A1) A typical desktop hard disk rotate at 7,200 revolutions per
    minute (RPM). A typical server hard disk spin at 10,000 or
    15,000 rpm to achieve sequential media transfer speeds. You
    can use hard disk model number to obtain disk RPM. For
    example, a typical Seagat disk Model # ST373455SS can
    provide following information:
    * ST - Brand identity
    * 3 - Form Factor (3 = 3.5")
    * 73 - Disk size / Capacity in GB i.e. 73GB
    * 4 - Reserved for future use
    * 5 - RPM ( 5 = 15k and 0 = 10K)
    * 5 - Generation
    * SS - Indicates interface i.e Serial Attached SCSI
    How do I find out hard disk model and serial number?
    Use any one of the following command from shell prompt to
    find out hard disk model number:
    $ cat /proc/scsi/scsi
    OR use scsi_id command to querys a SCSI device via the SCSI
    INQUIRY vital product data (VPD) page 0x80 or 0x83 and uses
    the resulting data to generate a value that is unique across
    all SCSI devices that properly support page 0x80 or page 0x83.
    $ /sbin/scsi_id -g -p 0x80 -s /block/sdd
    $ sudo grep -i sdd /var/log/boot.log
    OR use sginfo / scsiinfo command from sg3_utiles package, enter:
    # sginfo -a /dev/sdd | more
    Q12) when zombie process fully cleared?
    A1) When the server gets restarted!
    A2) Do a ps and identify the zombie processes
    # ps -el | grep 'Z'
    Occasionally, these processes are in such a state that the
    only way to get rid of them is to reboot to clear them.
    In most cases, you can get rid of a zombie by normal means,
    "kill -15 zombie PPID", "kill -9 zombie PPID".
    Q13) how do you configure linux system as a router?
    A1) Give the following command
    echo 1 > /proc/sys/net/ipv4/ip_forward
    A2) above anwser also write,
    but must me know this,
    vi /etc/sysctl.conf
    # Controls IP packet forwarding
    net.ipv4.ip_forward = 1
    save &
    sysctl –p
    Q14) Which priority has the process?how do u view?
    A1) nice command is used to find the priority
    A2) Each process has a niceness value associated with it, which
    is what the kernel uses to determine which processes require
    more processor time than others. The higher the nice value,
    the lower the priority of the process. In other words, the
    nicer” the program, the less CPU it will try to take from
    other processes; programs that are less nice tend to demand
    more CPU time than other programs that are nicer.
    The priority is noted by a range of -20 (the highest) to 20
    (the lowest). Using ps, you can see the current nice value
    of all programs:
    # ps axl
    4 0 1 0 16 0 2648 112 - S ?
    0:01 init [3]
    1 0 2 1 34 19 0 0 ksofti SN ?
    0:02 [ksoftirqd/0]
    5 0 3 1 10 -5 0 0 worker S< ?
    0:00 [events/0]
    You can see that init has a nice value of 0, while other
    kernel tasks associated with PID 2 and 3 have a nice value
    of 19 and -5 respectively.
    Typically, a program inherits its nice value from its
    parent; this prevents low priority processes from spawning
    high priority children
    Q15) Any one example of uninteruptable sleeping process?
    A1) init (PID 1)
    Q16) how many limitations of under directories in ext2/3 linux
    file system?
    A1) Ext2 Limits
    Max file size: 2-64 TiB
    Max number of files: 10 raised 18
    Max filename length: 255 characters
    Max volume size: 16-32 TiB
    Allowed characters in filenames: Any byte except NULL and '/'
    Ext3 Limits
    Max file size: 2 TiB
    Max number of files: Variable, allocated at creation time[1]
    Max filename length: 255 bytes
    Max volume size: 2 TiB – 16 TiB
    Allowed characters in filenames: All bytes except NULL
    Q17) what is a superblock ?
    A1) A superblock is a record of the characteristics of a
    filesystem, including its size, the block size, the empty
    and the filled blocks and their respective counts, the size
    and location of the inode tables, the disk block map and
    usage information, and the size of the block groups.
    Q18) what is the command to check network interfaces in our system?
    how to set etho to 10 full duplex speed?
    A1) ifconfig, ifconfig -a, ip dev ls,
    ethtool -s eth0 speed 10 duplex full
    to watch the info on eth0 ( mii-diag --watch eth0 )
    Q19) 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?
    A1) 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 >
    Q20) what is soft mount and hard mount? i have to make permanent
    nfs mount permanent what shall i do?
    A1) to make permanent nfs mount, write it into /etc/fstab
    Server nfsmount mountpoint filesystem defaults 0 0 /var/ftp/pub /mnt nfs defaults 0 0
    A2) This is a UNIX terminology as to what the client does when
    it can't talk to an NFS Server. If you just mount a file
    system without specifying hard or soft, the default is a
    hard mount. Hard mounts are preferable because of the
    stateless nature of NFS. If a client sends an I/O request to
    the server (such as an ls -la), and the server gets
    rebooted, the client will wait until the server comes back
    on line. This preserves data transfers in the event of a
    server failure. There are disadvantages to this, as a simple
    mount request could hang. A soft link will return with an
    error and fail. This kills the wait time, but can cause
    problems with data transfers.
    To make permanent nfs mount, the above answer is right
    Q21) what is major and minor?
    A1) Major number
    A number indicating which device driver should be used to
    access a particular device. All devices controlled by the
    same device driver have a common major device number.
    Minor number
    A number serving as a flag to a device driver.The minor
    device numbers are used to distinguish between different
    devices and their controllers.
    # ls -l /dev/sda1
    brw-rw---- 1 root disk 8, 1 2008-09-04 08:28 /dev/sda1
    rigel:~# ls -l /dev/sda2
    brw-rw---- 1 root disk 8, 2 2008-09-04 08:28 /dev/sda2
    You can see the major and minor device number (8,1) and
    (8,2) in the ls listing for /dev/sdax
    # ls -l /dev/scd0
    brw-rw---- 1 root cdrom 11, 0 2008-09-04 08:28 /dev/scd0
    You can see the major and minor device number (11,0)in the
    ls listing for /dev/scd0
    Q22) what is the command to make a process to run in the
    background from foreground?
    A1) To make the command run in the background suppose the
    Command is "command_name" then the syntax for the same will
    be such as follows;
    [root@neo root]# command_name &
    Q23) 1.what is Kernel parameters? many cpu have use in your machine?
    A1) Kernal parameters are nothing but all the parameters in
    /etc/system hear we can edit according to our requrement.
    to check the how many cpus in the machine jus type this command
    to check the cpu speec #psrinfo –v
    A2) 1.kernel parameters
    parameters provide mechanisms to adjust the functiong of linux kernel.
    the sysctl command used to view kernel parameters.
    2.simply type in root
    # cat /proc/cpuinfo
    Q24) 1.I want to change runlevel but the Users shall not be disturbed?how?
    2.Disk have 5gb disk utilization even though files unable to reate, why?
    3.what are the internal and external command in linux?
    4.sar command o/p? list the open files?
    6.what is kernel compiling?
    7.How do u See complete configuration in ur system? will u make a daily updates with cron daily?
    9.which port is associated with ttys0?
    10.specific some problems linux admin(if u are linuxadmin)faced
    And how did u overcome it?
    A1) 1. For changing the runlevel you should have to go in
    /etc/inittab. There you can change the runlevel what you
    want.It will not affecting current user. After restarting
    system your system will boot in which run level you have set.
    3. Internel command means whichever command are builtin the
    system BIOS. And External command means Which are
    nonbuiltin.It outside the shell. It require shell.
    4. VMstat & sar are showing the free memory of the system.
    5. ls command is use list a file & cat & vi is to open a file.
    A2) 1) Same answer as above
    2) Question not understood, may be ACLs
    3) It is not BIOS,
    A built-in (internal/resident) command is one that is
    contained within the bash tool set and execute faster than
    external commands.
    An non-built-in (external/non-resident) command is a command
    outside the shell and requires a $PATH (environmentvariable) to findit.
    4)Displays the activity for the CPU
    # sar
    Linux 2.6.18-6-686 (server.domain.local) 09/16/2008
    11:31:56 AM LINUX RESTART
    5) # lsof
    6)The Linux kernel is a complex program which provides the
    underlying services to the rest of a Linux distribution. But
    it is easy to add new features or improvements to it,
    requiring a kernel recompiling. There are three reasons for
    a kernel compile. Firstly, you may have some hardware that
    is so new that there's no kernel module for it in on your
    distribution CD. Secondly, you may have come across some
    kind of bug which is fixed in a revision of the operating
    system. Lastly, you may have some new software which
    requires a newer version of the operating system.
    7)A vague question
    8) Suppose we have a daily update script called
    Copy the script to /etc/cron.daily/
    # cp dailyupdate.script /etc/cron.daily/
    Make the file executable
    # chmod +x /etc/cron.daily/
    9) COM1
    10) Depends...
    A3) 4) Detailed sar output
    Linux 2.6.18-6-686 (server.domain.local) 09/16/2008
    11:31:56 AM LINUX RESTART
    11:35:01 AM CPU %user %nice %system
    %iowait %steal %idle
    11:45:01 AM all 0.71 0.00 0.19
    0.18 0.00 98.92
    11:55:02 AM all 1.53 0.00 0.19
    0.26 0.00 98.02
    Average: all 1.12 0.00 0.19
    0.22 0.00 98.47
    A4) 1. use init , at runtime.
    2. disk quota has been set and reached for the current user.
    3. same as above
    4. same as above
    5. same as above
    6. lay man definition, adding support for required hardware
    and modules in the Linux kernel.
    7. sysreport, question too generalized,
    8. same as above
    9. same as above
    10. :)
    Q25) what is user mode & kernel mode?
    The kernel-mode programs run in the background, making sure
    everything runs smoothly - things like printer drivers,
    display drivers, drivers that interface with the monitor,
    keyboard, mouse, etc. These programs all run in such a way
    that you don't notice them.
    When the computer boots up, Windows calls the KERNEL, the
    main kernel-mode program that allows all the other programs
    to run, even the user-mode programs.
    These are the programs that you run when you want specific
    programs - e.g., MS Paint, MS Word, and Calculator. These
    are heavily restricted, as to not crash the system. Windows
    uses memory-protection services offered by the processor to
    prevent malicious programs from interfering with the rest of
    the system and corrupting it.
    A2) A process can run in two modes:
    1.User Mode.
    2.Kernel Mode.
    1.User Mode:
    =>A mode of the CPU when running a program.
    =>In this mode ,the user process has no access to the
    memory locations used by the kernel.When a program is
    running in User Mode, it cannot directly access the kernel
    data structures or the kernel programs.
    2.Kernal Mode:
    =>A mode of the CPU when running a program.
    =>In this mode, it is the kernel that is running on behalf
    of the user process and directly access the kernel data
    structures or the kernel programs.Once the system call
    returns,the CPU switches back to user mode.
    When you execute a C program,the CPU runs in user mode till
    the system call is invoked.In this mode,the user process has
    access to a limited section of the computer's memory and can
    execute a restricted set of machine
    instructions.however,when the process invokes a system
    call,the CPU switches from user mode to a
    more privileged mode ­the kernel. In this mode ,it is the
    kernel that runs on behalf of the user process,but it has
    access to any memory location and can execute any machine
    Instruction. After the system call has returned,the CPU
    switches back to user mode.
    Kernel mode, also referred to as system mode, is one of the
    two distinct modes of operation of the CPU in Linux. When
    the CPU is in kernel mode, it is assumed to be executing
    trusted software, and thus it can execute any instructions
    and reference any memory addresses (i.e., locations in
    memory). The kernel (which is the core of the operating
    system and has complete control over everything that occurs
    in the system) is trusted software, but all other programs
    are considered untrusted software.
    User mode is the normal mode of operating for programs, web
    browsers etc. They don't interact directly with the kernel,
    instead, they just give instructions on what needs to be
    done, and the kernel takes care of the rest. Kernel mode, on
    the other hand, is where programs communicate directly with
    the kernel. A good example of this would be device drivers.
    A device driver must tell the kernel exactly how to interact
    with a piece of hardware, so it must be run in kernel mode.
    Because of this close interaction with the kernel, the
    kernel is also a lot more vulnerable to programs running in
    this mode, so it becomes highly crucial that drivers are
    properly debugged before being released to the public
    Q26) what is the diff b/w ext2 and ext3?
    A1) ext3 is the advanced version of ext2
    this journaling feature is very much useful while
    retrieving data and writing data into a File System
    Latest versions of all Linux flavors are coming with ext3
    compatible file systems.
    A2) ext 2 & ext3 are the two file systems in linux.ext 2 will
    take more time while logon the system. this is bcoz ext2
    will check all harddisk peripherals at the time of switch on
    your sytem. But ext3 is less time consuming,bcoz instead of
    checking all harddisk peripherals it will check only the
    bootloader peripherals.
    Q27) what is initrd image?
    A1) initrd image is the initial ram disk image While the system
    getting booted the kernel image will get loaded into the main
    memory after POST to improve I/O performance.this initrd image
    will contain the same version number of kernel and if we face any error
    in booting regardingthis initrd we can reinstall it with 'mkinitrd' command
    A2) initial RAM disk (initrd) is a temporary root file system
    that is mounted during system boot to support the two-state
    boot process. The initrd contains various executables and
    drivers that permit the real root file system to be
    mounted, after which the initrd RAM disk is unmounted and
    its memory freed. In many embedded Linux systems, the
    initrd is the final root file system
    A3) initrd image is a image file which has initial modules which
    are loaded in to the kernel while booting.
    Q28) what is jumbi process? Oracle
    A1) its a dead process it's parent process has been killed abruptly.
    A2) zoombie process or defunct process. - Process that finish execution
    Or we can say the process died but still it has entry in the
    process table.
    A process finished execution but parent of that process is
    Not ready to accept the exit status from it . At that time
    process go to zoombie state.
    Q29) My machine is running half duplex mode how to change half
    duplex to full duplex? ORACLE
    A1) [root@ns2 ~]# mii-tool -V
    mii-tool.c 1.9 2000/04/28 00:56:08 (David Hinds)
    eth0: negotiated 100baseTx-FD flow-control, link ok
    [root@ns2 ~]# ethtool -s eth0 duplex half autoneg off
    [root@ns2 ~]# mii-tool -V
    mii-tool.c 1.9 2000/04/28 00:56:08 (David Hinds)
    eth0: 100 Mbit, half duplex, no link
    [root@ns2 ~]# mii-tool -V
    mii-tool.c 1.9 2000/04/28 00:56:08 (David Hinds)
    eth0: 100 Mbit, half duplex, link ok
    Q30) some one is asking my machine is slow what is your steps? ORACLE
    A1) The increase in the size of SWAP partition may show you the
    little effect in increasing the system speed and better run
    in Single user mode rather than GUI mode
    A2) use top command, then check which process use the most
    resource and find the problem.
    A3) Re-read all process
    #killall –HUP
    Q31) what is mean by system calls INFOTECH
    A1) 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.
    Q32) What is trusted/untrusted operating system
    A1) As per my perspective , I used to say any/all UNIX flavors
    rather than MS WINDOWS
    Because of
    1. File/Directory permission (Action:Read/Write/Execute,
    permissions can be given on behalf of the particular
    2. All the unix configuration as files rather than
    Registry (windows)
    a. which cause the application to fail when a newer
    or incompatible dynamic library is installed.
    b. Some times you may need to restart the entire
    system to update the changes with registry.
    3. Linux Strong password protection. It won't get booted
    (Drop you @ the GUI) without the successful
    authentication (even though you don't have any more
    users rather than admin/root).In Linux setting
    password to the admin/root users is must during the
    installation itself.
    Where as in windows, let allow you to leave the
    password as blank for admin/other user, System also
    booting without authenticating.
    4. Linux is open source, free under GNU. It doesn't mean
    that its only free to install or use, but in fact you
    can have these source codes and they are allowing you
    to change it and redistribute it.
    Windows is Lincesed os. Windows is developed by
    5. Linux is more secure, windows is less secure than
    linux in case of virus, worms.
    Because in Linux all the files/directory won't get
    executable permission, Perhaps you need to set it
    manually. Though by default all the incoming trojen,
    virus, malwares and worms won't affect the system.
    6. Distribution
    Linux : Linux has many distributors like Radhat,
    mandrake, Corel etc
    Windows : whereas windows has only Micrsoft.
    7. Run Level
    Linux works on both GUI & Console mode (Checkout the
    various run levels runlevel 0 - runlevel 6 Generally
    known as init level)).
    Windows : Only GUI.
    8. By default LINUX have multiuser, multitasking,
    multiprocessing, multiprogramming features. Perhaps
    this will not be available on windows(Except some
    versions), In that case you need to PAY & BUY
    the extra features in windows.
    9. You can play around the Linux through LIVE CDS on a
    Windows machine.
    Only is a live CD that runs over windows, in RAM,
    and doesn't change your system at all..the other is
    an install disk. I've used the live CD on two XP
    machines and they both ran flawlessly. When you
    want to quit, just go to logout under system tools,
    and shut down.
    Linux will turn itself off, eject the disk, and turn
    of your PC.
    Remove the disk, boot up, and you're running your
    Windows again.
    This is the way we are checking the newly bought
    NIC/others hardwares support with all the Linux
    distributors. Once it got detected, its very easy to
    get the device driver names and other details about
    that new hardwares, then compile the new kernel
    image (bzImage) on your own build version systems.
    Q33) Working in Linux/Unix platform, if any command dose not
    work, say # ls reports as command not found.
    what to do? GOOGLE
    A1) Need to check the path first body ....
    A2) reinstall that shell
    A3) Check whether PATH variable as got the entry /bin
    It should be something like this
    [root@bc ~]# echo $PATH
    Q34) in unix how to change old name to new name
    A1) mv // for rename the file in the same
    mv // for rename and
    move the file in other diretory.
    A2) 1. open the file /etc/sysconfig/network and change the
    parameter HOSTNAME= to new name.
    2. restart the network services.
    3. open the file vi /etc/hosts, and change the old name to
    new name. localhost.localdomain
    A3) mv
    [root@localhost]# touch file1 //created a file named file1
    root@localhost]# ls //displays the file created
    [root@localhost]# mv file1 file2 //command to rename file1
    [root@localhost]# ls //displays the renamed file
    A4) see there is no rename command in unix ,
    so what u can use is "move" (mv) command
    mv "(absolute path) old file name" "new file name
    A5) rename
    Q35) what is the standard output in a file as well as disply it
    on the terminal options like
    A)pr B) tail C) tee D)nl
    A1) tail as it display ten current line
    tail -f
    option with this
    tail -f -n 100
    A2) I think, framing the question should be like
    "What is the command used to write to the standard output
    as well as to a file simultaneously ?
    Answer) tee
    It is a command that deals with pipes in unix. It
    redirects the output of a command to an other command and
    at the same time it redirects to a file also.
    Q36) what is command like " #(cd unixos; pwd) " tell me OUTPUT
    A1) first it will change the directory to unixos and then gives
    the output as //unixos
    A2) it is two commands runnung one by one.first the cd unixos
    command will be executed,then the present working directory
    will the output will be showing the presentworking
    dirctory that is unixos dir.
    A3) WRONG when I hit this command no output or error is printed
    Q37) in unix how to change old name to new name

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