Get a free shell account online


A shell is an utility from where you can access Linux/*Nix servers from any where and execute the commands/scripts etc.

This post is for the users who are new to linux/Nix and want to feel/work on the Linux with out installing on the system. "" is free online BSD(Berkeley Software Distribution) server where you can request a shell account and explore your self.

There are so many free shell providers on net but most of the servers/service providers will not give you free account simply, you have to prove your self to them that you are not a spamer and you are really in need of shell account to explore Unix.

Here are some advantages:

  1. No need to install any unix systems.
  2. Good for beginers.
Some disadvantages:

  1. You can work on only limited commands provided by the system administrator.
  2. Require any SSH clients(such as Putty) and internet connection.
Here are the links from where you can get your free Shell accounts

  1. (I personally used their service and its preaty good)
Please comment on this so that I can improve the blog quality.

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  • Distro's


    This is my first post on Distro's. To discuss about Distributions, there is lots and lots of information about them which is beyond this blog. But I will try to cover as much good and best distros in the market on weekly basis.

    To start with.. what is a Distro actually?
    A "Linux distribution" (also called GNU/Linux distribution by some vendors and users) is a member of the family of Unix-like software distributions built on top of the Linux kernel. A distro some times refferd as "Distribution" or "Flavor".

    1. For General public purpose(like Ubuntu & Fedora).
    2. For Corporate purpose(like Cisco Linux & Oracle Linux).
    3. For Regionality purpose(like swecha Linux for People whose mother tongue is Telugu).
    4. For Basic routing purpose(like Linux router project).
    A distro is nothing but linux kernel(in general it is considerd as core of operating system)+Applications(such as mail clients,servers, browsers office suite etc).

    Suppose if we say Redhat linux it is equal to Linux kernel developed by linus torvalds + Applications developed by Redhat people.
    For your information here are some details about Distro.
    There are more than 500 Distro's in Linux followed by Unix with 150 flavors then with Windows around 50

    Please keep an eye on this session to see coming Distro's.

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  • 10 Commandments !! U like it for sure!!


    This is a guest post by Praveen


    =>1 People are illogical, unreasonable, and self-centered. Love them anyway.

    =>2 If you do good, people will accuse you of selfish, ulterior motives. Do good anyway.

    =>3 If you are successful, you will win false friends and true enemies. Succeed anyway.

    =>4 The good you do today, will be forgotten tomorrow. Do good anyway.

    =>5 Honesty and frankness make you vulnerable. Be honest and frank anyway.

    =>6 The smallest men and women with the smallest minds can shoot down the biggest men and women with the biggest ideas. Think big anyway.

    =>7 People favor underdogs, but follow only top dogs. Fight for a few underdogs anyway.

    =>8 What you spend years building may be destroyed overnight. Build anyway.

    =>9 People really need help, but may attack you if you do help them. Help people anyway.

    =>10 Give the world the best you have and you’ll get kicked in the teeth. Give the world the best you have anyway.

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  • Monitoring users - I


    User-management is always one of the basic tasks for Linux administrators, here we are going to see some basics user related "Monitoring Commands".

    1) "finger" is a command which will give full details about user properties such as name, login, shell what he is using etc.


    #finger username

    [root@localhost ~]# finger root
    Login: root Name: root
    Directory: /root Shell: /bin/bash
    On since Sat Jun 6 19:20 (EDT) on tty1 4 hours 12 minutes idle
    On since Sun Jun 7 02:18 (EDT) on pts/0 from :0.0
    On since Sun Jun 7 03:48 (EDT) on pts/1 from :0.0
    16 minutes 9 seconds idle
    New mail received Sun Jun 7 04:02 2009 (EDT)
    Unread since Sat Jun 6 22:17 2009 (EDT)
    No Plan.

    Here you can see so many user related information
    one security information you can see is when he loged in last time and from where he loged in etc.

    2)"id" is one more command which will show the user details such as his primary group and his secondary group.


    #id username


    [root@localhost ~]# id root
    uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel) context=root:system_r:unconfined_t:SystemLow-SystemHigh
    [root@localhost ~]#

    3)"chage" is one more command which is used to see user related "threshold details" such as user disable time etc.


    #chage -l username


    [root@localhost ~]# chage -l root
    Last password change : Jun 06, 2009
    Password expires : never
    Password inactive : never
    Account expires : never
    Minimum number of days between password change : 0
    Maximum number of days between password change : 99999
    Number of days of warning before password expires : 7
    [root@localhost ~]#

    4)"who" is one more command to see who other people logged in and from where they logged in.



    [root@localhost ~]# who
    root tty1 2009-06-06 19:20
    root pts/0 2009-06-07 02:18 (:0.0)
    root pts/1 2009-06-07 03:48 (:0.0)
    [root@localhost ~]#

    5)"w" is one more command which is similar to "who" command but will give some more details.


    [root@localhost ~]# w
    06:36:49 up 11:23, 3 users, load average: 0.54, 0.38, 0.42
    root tty1 - 19:20 4:27m 0.69s 0.69s -bash
    root pts/0 :0.0 02:18 0.00s 0.16s 0.02s w
    root pts/1 :0.0 03:48 31:25 0.10s 0.10s bash
    [root@localhost ~]#

    6)"groups" is one more wonderful command which will show which user belongs to what groups, we can say its a subset of id command


    #groups username


    [root@localhost ~]# groups root
    root : root bin daemon sys adm disk wheel
    [root@localhost ~]#

    7)"users" is one more monitoring command to see which users loged in at present in to the system


    [root@localhost ~]# groups root
    root : root bin daemon sys adm disk wheel
    [root@localhost ~]#

    Please add if you know some other user related monitoring commands.

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  • RAID01 Vs RAID10


    So what is the difference between RAID01 and RAID10?
    This is bit tricky question, Recently I came to know about this one in an interview. so do both are same?
    No both are not same.

    When we are dealing with RAID01 we are actually implementing RAID0 first then RAID1 on it. Ok little bit confused?
    Let me put it in this way RAID0 is nothing but stripeset writing of data and RAID1 is Mirring of data on to disks.For example lets take 8 disks, so first we are writing whole data on 4 disks then we are mirring it on to remaining disks.
    Where as in RAID10 we are first mirring disk and then striping data on mirrered disks
    In general RAID01 is "a mirrior of 2 strips" and RIAD10 is "a single strip on mirrered disks"

    So here one more question arises... which one is good?
    RAID10 is good, the difference is that the chance of system failure with two drive failures in a RAID 0+1 system with two sets of drives is (n/2)/(n - 1) where "n" is the total number of drives in the system. The chance of system failure in a RAID 1+0 system with two drives per mirror is 1/(n - 1). So, using the 8 drive systems shown in the diagrams, the chance that loosing a second drive would bring down the RAID system is 4/7 with a RAID 0+1 system and 1/7 with a RAID 1+0 system.

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  • Linux interview questions :FTP



    One of my friend asked me why there is no answers for So many interview questions, basically most of the interview questions which are on this site are the interviews which happened to me so. At that time I am not able to Answer some of the questions, so from today on words I will try to post all the interview questions with answers, If you feel these answers are wrong you can feel free to comment with proof so that i can modify my posts.

    1)What is the difference between TFTP and FTP servers?
    A)Both are file transfer servers but slight difference is TFTP server uses UDP protocol and FTP uses TCP protocol. TFTP is good for slow connection paths.

    2)What is the port no for FTP?
    A)20 for Data and 21 for Control(normally when an interviewer ask's ftp port number just say 21.

    3)What is the port no for TFTP?

    4) How to restrict users to their home directories?
    By setting up "chroot_local_user=YES".

    5)How to restrict total number of users accessing FTP server?
    If Vsftpd is running under xinted service, then you can use xineted to get per-service per IP connection limits or
    A2) If you run vsftpd in "standalone" mode with the "setting listen=YES", then
    you can investigate the setting (e.g.) : "max_clients=10"

    6)I want to copy multiple files with out prompting for any info, how can I do that one?
    A)Simply do "ftp -i ftpserver" this command will suppress any info displayed on ftp server.
    or you can just type prompt ftp prompt to suppress info messages have a look here.

    7) Some times Local users cannot log in. How to resolve this issue?
    Check "local_enable=YES" in your /etc/vsftpd/vsftpd. conf to allow local users to log in.

    8) How do we integrate with LDAP( Lightweight Directory Access Protocol )users and login?
    Use vsftpd's( Very Secure FTPD) PAM(Pluggable Authentication Modules) integration to do this, and have PAM authenticate against an LDAP repository.

    9) Can we host different ftp sites on single machine, I mean virtual hosting concept like Apache?
    Yes. If you integrate vsftpd with xinetd, you can use xinetd to bind to several different IP addresses. For each IP address, get xinetd to launch vsftpd with a different config file. This way, you can get different behavior per virtual address.
    A2) Alternatively, run as many copies as vsftpd as necessary, in standalone
    mode. Use "listen_address=x.x.x.x" to set the virtual IP.

    10) How to restrict different users with different permissions in vsftpd
    A) By setting up "user_config_dir" entry in "vsftpd.conf".

    11)How to change vsftpd default port?
    A)By setting "listen_port" option in "vsftpd.conf".

    12) Vsftpd is reporting times as GMT times and not local times!. How to resolve this?
    This behavior can be changed with the setting "use_localtime=YES".

    13) How to disable certain FTP commands?
    A) There are some individual settings (e.g. dirlist_enable) or you can specify a complete set of allowed commands with "cmds_allowed".

    14) How does vsftpd support per-IP limits?
    If you are running vsftpd standalone, there is a "max_per_ip" setting.
    A2) Yes. If you are running vsftpd via xinetd, there is an xinetd config variable "per_source".

    15) How Does vsftpd can do bandwidth limiting?
    settings such as "anon_max_rate" and "local_max_rate" can be used to set this limits.

    16) How to restrict some IP's not use my FTP server?
    vsftpd can integrate with tcp_wrappers (if built with this support). It is enabled with the setting "tcp_wrappers=YES".

    17) Does vsftpd support IPv6?
    Yes, as of "version 1.2.0".

    18) Help! I'm getting messages along the lines of "500 OOPS: vsf_sysutil_bind" when trying to do downloads (particularly lots of small files).
    A) "vsftpd-1.2.1"
    should sort this out.

    19) Can we use vsftpd to hiding or denying certain files?
    Yes. Look at the hide_file and deny_file options.

    20)How you can check if there is any syntax error in vsftpd.conf file?
    A)Just type vsftpd with out quoats.

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  • Linux Interview Questions: Experienced


    1)How to implement Squid proxy?
    2)How to see bandwidth used by ftp user?
    3)ow to implement Squid as reverse proxy?
    4)How to see logs of Squid proxy?
    5)How to see cache in Squid proxy?
    6)How to clear Cache in Squid proxy?
    7)Totally how many configuration modules are there in Squid proxy?
    A)nearly some 127 modules in squid proxy
    8)What is the authentication used in Samba when it is used as PDC?
    9)Where is the logs present for samba PDC server?
    10)Some of the logs in my system are not time stamped how to resolve this ?
    11)How to see what is the encryption used by ssl?
    11)How to host different domains on with different ip add on single system?
    12)How to assigned different ip add to single interface?
    13)How to assign different ip addresses to single interface? what is the default gateway to each ip address?

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  • Linux Interview questions:Experienced


    1)What is the difference between Xen and VMware?
    A)XEN : Xen is an open-source virtualization solution. The Xen hypervisor acts as a thin layer between the hardware and the operating system, allowing multiple virtual servers to run simultaneously on a single physical server. Each virtual server acts independently of the others, with its own allocated area of RAM and virtual disks.
    VMware : VMware is a company that provides virtualization software for x86-compatible computers.

    2)Can we install HPUX( (Hewlett Packard UniX) on Vmware?
    A)No. Because HPUX can be installed only on PA-RISC or Itanium and Vmware can not emulate this hardware.
    3)How to use SAMBA as PDC(Primary Domain Controller)?
    4)What is IPchains?
    A)Ipchains is a utility for Linux that System Administrators can use to create and modify the ruleset that is used for their host based firewall. These rules are used by a system to decide whether or not it is going to allow a specific remote connection.
    5)What is the difference between IPchains and IPtables?
    IPchains : Ipchains is a utility for Linux that System Administrators can use to create and modify the ruleset that is used for their host based firewall. These rules are used by a system to decide whether or not it is going to allow a specific remote connection.
    IP tables : Iptables is a generic table structure that defines rules and commands as part of the netfilter framework that facilitates Network Address Translation (NAT), packet filtering, and packet mangling in the Linux 2.4 and later operating systems.
    6)Explain me how we can use parted command to create partitions ?
    7)What is hard NFS(Network File System)? mount and soft NFS mount?
    8)Explain briefly about Linux Booting process?
    9)What is the difference between TCPdump and Nmap?
    10)How to create EXT3 and EXT2 file system?
    11)What is the difference between ext2,ext3 and ext4?
    12)How to extend LV(Louis Vuitton)?
    13)How to see how many VG's are there?
    14)Explain the process of configure Apache.
    15)How many types of chains are there in IPtables and what are they explain each?
    16)What is super block?
    17)What is INODE limit? If the file system reaches that limits how to resolve that?
    A)Inode is a unique number given to a file in Unix OS. Every file in Unix has a inode number. unix treats directories/folders as a file so they are also having a inode value.
    18)What are ACL's in Linux how to implement it in Linux?
    19)How to take backup to Tape-drives?
    20)How to rectify if tape drive file(hardware file) is missing?
    21)What is the difference between RAID01 and RAID10?
    22)When using RAID in which cases will you use RAID1 and which cases you will use RAID5?
    23)How to implement password less SSH logins?
    24)How a user can change a password?
    25)How can you get info that my last command executed properly?

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  • Mail system explained



    Send mail is one of the old and widely used mail delivery agent/Mail system. Agent Description from Wikipedia
    1 Mail User Agent(MUA) An e-mail client (also mail user agent (MUA) or e-mail reader) is a frontend computer program used to manage e-mail.
    2 Mail Transfer Agent(MTA) A mail transfer agent (MTA) (also called a mail transport agent, message transfer agent, or smtpd (short for SMTP daemon), is a computer program or software agent that transfers electronic mail messages from one computer to another.The term mail server is also used to mean a computer acting as an MTA that is running the appropriate software. The term mail exchanger (MX), in the context of the Domain Name System formally refers to an IP address assigned to a device hosting a mail server, and by extension also indicates the server itself.
    3 Mail Delivery Agent(MDA) A Mail delivery agent (MDA) is software that delivers e-mail messages after they have been accepted on a server, distributing them to recipients' individual mailboxes.
    4 Mail Access Agent(MAA) A way of remotely accessing a mail-spool, for example POP3 or IMAP.

    A short description how a Mail communication will work:

    Here I will take an example how a mail from John( to his friend Jelo( will be delivered.

    Step1:first John has to write a e-mail by specifying who is the receiver of this mail(in this case it is Jelo).So  things like composing mails will be taken care by MUA.this MUA( A mail client such as MS outlook,Thunder-bird etc) knows how to deals with mail transportation,Once Jhon press send and receive in e-mail client,MUA initiate talk with its MTA(A SMTP server which is listening  on 25 port for receiving mails).

    Step2:Once MTA(such as SEND-MAIL,Qmail,Post-Fix etc) get the request from MUA, MTA will take care of all the activity such as communicate with MUA and fetching mails from MUA etc.

    Step3:Once MTA got the mails from MUA, it has to segregate all the mails according to different domains. for example Jhon is sending 4 mails(one to, one to, one to and one to this MTA will segregate these 4 mails in to 3 pools(jelo and jennie mails will be pooled in same pool so that they will be delivered to,anne mail will be pooled to and raja's mail will be pooled to

    Step4:Once the segregation has happened MDA(nothing but again its a send-mail which will take care of )will delivered these mails to respective MAA(such as Dovecot ).

    Step5:Now suppose mail has delivered to their respective MAA's. Once the mail reaches, MAA will try to segregate the mails according to users(here for example Jelo and Anne mails has arrived to MAA) then this MAA will put the mails of Jelo and Anne in respective mails boxes in a Mail Store(MS) as shown in Figure.

    Step6:Now MUA will come in to picture in downloading these mails from MAA, so MUA will communicate with MAA and download the mails to MUA(like outlook and thunder-bird).

    Please comment on this and we will post basic configuration of Sendmail in my comming posts.

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  • Linux Interview Questions: Sendmail


    The below questions are not my own, you can reach the author at 
    -Ian! D. Allen - -
    A common misconception: the place/protocol you use to fetch your email
    is the same place/protocol that you use to send your email:
       - sending email uses SMTP
       - reading email uses POP3 or IMAP
       - they can be completely separate machines
    Q: T/F, unlike POP3, SMTP can be used to both send and receive email.
    Q: T/F, unlike SMTP, POP3 can be used to both receive and send email.
       - may be completely different servers
       - though note POP-before-SMTP (SMTP-after-POP) requires coupling:
   (section 3.3)
       "Requiring a POP [POP3] authentication (from the same IP address)
        within some amount of time (for example, 20 minutes) prior to the
        start of a message submission session has also been used, but this
        does impose restrictions on clients as well as servers which may
        cause difficulties.  Specifically, the client must do a POP
        authentication before an SMTP submission session, and not all clients
        are capable and configured for this.  Also, the MSA must coordinate
        with the POP server, which may be difficult.  There is also a window
        during which an unauthorized user can submit messages and appear to
        be a prior authorized user."
    Q: Describe briefly how POP-before-SMTP works to authenticate an SMTP session.
    MUA - Mail User Agent (email client)
      - the user's interface to the protocols - "presentation layer"
      - usually gives access to functionality of both MTA and MRA/MAA
        - but may not itself implement any protocols (may read/write file system)
       "An e-mail client, also called a Mail User Agent (MUA), is a computer
        program that is used to read and send e-mail.
        Originally, the MUA was intended to be a simple program to read the user's
        mail messages, which the mail delivery agent (MDA) in conjunction with
        the mail transfer agent (MTA) would transfer into a local mailbox.
        The most important mailbox formats are mbox and Maildir. These rather
        simple protocols for locally storing e-mails make import, export and
        backup of mailfolders quite easy.
        E-mails to be sent would be handed over to the MTA, perhaps via
        a mail submission agent [MSA], therefore an MUA would not have to
        provide any transport-related functions.
       *Since the various Microsoft Windows versions intended for home use never
       *provided an MTA, most modern MUAs have to support protocols like POP3
       *and Internet Message Access Protocol (IMAP) to communicate with a remote
       *MTA located at the e-mail providers machine."
     - user agents (MUAs) are user-visible email clients of all descriptions
     - e.g. mutt, "mail", "Mail", "mailx", pine, elm
     - e.g. KMail, Eudora, MS Outlook
     - e.g. web-browser email (Netscape Messenger,Mozilla,Thunderbird)
     - e.g. webmail, Horde, SqurrelMail

    Q: Briefly describe the function of a mail system MUA.
    MSA - Mail Submission Agent
       "acts as a submission server to accept messages from MUAs, and either
        delivers them or acts as an SMTP client to relay them to an MTA."
      - enforce policy (no open relay)
      - enforce standards (no forged headers, etc.)
      - enforce filtering (SpamAssassin, etc.)
      - may modify messages (section 8 of RFC)
    Q: Briefly describe the function of a mail system MSA.
    MTA - Mail Transfer Agent (mail server, mail exchange server)
       "A process which conforms to [SMTP-MTA], which acts as an SMTP server to
        accept messages from an MSA or another MTA, and either delivers them or
        acts as an SMTP client to relay them to another MTA."
       "It receives messages from another MTA (relaying), a mail
        submission agent (MSA) that itself got the mail from a mail user
        agent (MUA), or directly from an MUA, thus acting as an MSA
        itself. The MTA works behind the scenes, while the user usually
        interacts with the MUA.  The delivery of e-mail to a user's
        mailbox typically takes place via a mail delivery agent (MDA);
        many MTAs have basic MDA functionality built in, but a dedicated
        MDA like procmail can provide more sophistication."
     - transfers email between machines (other MTAs) via SMTP
     - Internet-facing, open ports: security issues
     - sendmail, postfix, qmail, exim
     - may have MDA ability to transfer email to user's mailbox
    Q: Briefly describe the function of a mail system MTA.
    MDA - Mail Delivery Agent
       "A Mail Delivery Agent (MDA) is software that accepts incoming e-mail
        messages and distributes them to recipients' individual mailboxes
        (if the destination account is on the local machine), or forwards
        back to an SMTP server (if the destination is on a remote server).
        A mail delivery agent is not necessarily a mail transfer agent (MTA),
        although on many systems the two functions are implemented by the
        same program."
     - Unix/Linux: /bin/mail, procmail 
    Q: Briefly describe the function of a mail system MDA.
    MRA/MAA - Mail Retrieval Agent / Mail Access Agent  - POP3 port 110  - IMAP-V4-R1 port 143
      - often built-in to mail clients (MUAs)
      - can be stand-alone
        - e.g. fetchmail gets the mail; MUA reads mail from file system
    Q: Briefly describe the function of a mail system MRA/MAA.
    Mail server comparison
      - see comparison near bottom
      - PUSH protocols - sending email: MTA - SMTP
      - PULL protocols - reading email: MRA/MAA - POP3, IMAP
     MDAs write local mailboxes; they may not implement Internet protocols
     (unless they have to forward off-machine without benfit of an MTA).
     Single-user PCs often don't run separate MTA or MRA/MAA programs.
     Your chose of mail reader (e.g. Pine, Elm, Outlook) itself PULLs your
     incoming email from a remote server (acting as an MRA/MAA) and then
     PUSHes your outgoing email to the remote server (acting as an MTA).
    Q: What is the difference between a PUSH protocol and a PULL protocol?
    Q: T/F, SMTP is a PUSH protocol.
    Q: T/F, POP3 is a PUSH protocol.
    Q: T/F, HTTP is a PUSH protocol.
    A History of MTAs
    I. Incoming - delivering your incoming email via SMTP:
    * Sending email into Unix/Linux machines:
      Unix/Linux was traditionally multi-user and ran its own MTA
      (e.g. sendmail) that accepted incoming SMTP connections.  Remote systems
      could use SMTP to drop off your email with your local MTA (sendmail),
      and the MTA would hand the email to an MDA (/bin/mail, procmail)
      to put it in your mailbox in the local file system.  Your MUA
      (e.g. /usr/ucb/Mail) would read the mail from your inbox (no need
      for POP3 or IMAP in any MUA).  There are a few different conventions
      for inbox formats so that many different MUAs can read your email,
      all without knowing POP or IMAP.
      - sendmail (running as root!) has had many security patches
        - the first Morris Internet worm (Nov 1988) used sendmail security holes
    Q: Why don't many Unix MUAs need to know how to run POP or IMAP?
      Current single-user Unix/Linux PCs often have a local-only MTA
      that handles the sending and delivery of local on-machine email but
      doesn't accept SMTP from off-site.  (Best to keep ports closed on
      Internet-facing machines!)
      On recent single-user Unix/Linux workstations, the MUAs mimic their
      Windows counterparts and include MRA/MAA features.  Your chosen MUA
      (e.g. Elm, Pine, Mutt) is responsible for fetching your email via POP3
      or IMAP (this is an MRA/MAA function); or, you use an intermediate
      MRA/MAA program such as "fetchmail" and your MUA reads the mail out
      of the local file system after the MRA/MAA has put it there.
      - no Internet-facing MTA means fewer open ports and fewer attacks
        - don't run an Internet-facing MTA if you don't need it
    * Sending email into MS Windows machines (or not):
      Windows had (has?) no MTA - you can't send an email to a Windows PC
      using SMTP.  Your personal Windows MUA has to fetch the email itself
      via POP3 or IMAP and keep a copy in the local file system.
     - no open ports for incoming email; no open mail port security issues
    * Note that MUAs that implement POP/IMAP typically store the email in
      the local file system in a format that only that MUA can handle.
      (Thunderbird can't use an Outlook mail folder, and vice-versa.)
      The concept of a common inbox format usable by different MUAs was lost.
    Q: T/F, the standards for inbox formats developed under Unix were adopted
       by MUAs on PCs, so that different MUAs can read the same inbox.
    II. Outgoing - sending your outgoing email via SMTP:
    * Unix/Linux machines have traditionally each had their own MTA (sendmail)
      that could directly deliver email on the Internet using MX record lookup.
      Every local Unix MUA would put email into a directory where the MTA
      (sendmail) would eventually pick it up and transfer it, retrying as
      necessary.  No MUA needed to know how to do SMTP; only the MTA did that.
      You could optionally tell your machine's MTA not to send mail directly
      to its destination via SMTP over the Internet, but to use a remote
      "smart" MTA that could accept your outgoing email and figure out
      how to deliver it.  (You have to use such a "smart" host here at
      Algonquin; since, you cannot connect to any off-campus SMTP servers.)
      The MTA on your machine would use SMTP to drop off the queued mail at
      the smart host, and the smart host would do the MX record lookup and
      final SMTP delivery.
      Since the local Unix MTAs were separately scheduled programs, you could
      queue email from a MUA into the file system even when your machine was
      not connected to the Internet.  The MUA or local MTA would queue up
      your email in the file system until your MTA was finally able to make
      a connection to deliver it off-machine.  (In the days of modems, the
      Internet connection was often made late at night when rates were lower.)
    Q: Why don't most Unix MUAs need to know SMTP?
      Current single-user Unix/Linux PCs now have MUAs that mimic their
      Windows counterparts - the MUAs ignore the file system and the local
      MTA and expect you to give the name of a remote "smart" MTA to which
      all email will be sent via SMTP for actual delivery.
      The Algonquin Linux lab has both types of mail systems:  Command-line
      email (e.g. the "mail" command) queues up mail for the local
      MTA (sendmail) to send.  (This is currently broken.)  GUI MTAs
      (e.g. Thunderbird, Mozilla) ignore the local file system and the local
      MTA and use a "smart" remote MTA (e.g.
      to deliver the mail.  (This supposedly still works.)
    * MS Windows has no local MTA - no program exists whose job it is just
      to deliver queued email.  Each MUA has to know how to do its own
      SMTP connection and each MUA has to be configured (separately!) with
      the address of a smart MTA to which it connects.  MUAs on Windows
      machines all contain networking code to drop off email at some "smart"
      MTA that does the actual delivery.  There is no local MTA queue and
      much duplication of SMTP code in all the MUAs.
      On Windows, it is up to each MUA to deal with what happens if the
      message being composed can't be dropped off right away at the remote
      smart MTA.  Better MUAs will queue the email for later transmission.
      Poor MUAs will tell you that your mail can't be sent.
    Q: Why do MUAs on Windows all need to know how to talk SMTP?
    Q: Unix/Linux mail user agents didn't need to know how to talk to SMTP
       servers - you never had to configure your "outgoing mail" preferences.
       All the Windows MUAs need to be configured with a mail server.  Why?

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  • Linux interview questions


    1)How to compile Apache?

    2)Users come to you and they will be saying mail server is very slow, what are the necessary steps you will take to resolve this issue?

    3)Which are the configuration files associate with DNS server and client?

    4)Where you will provide ISP details for your network?

    5)How you will configure Squid proxy?

    6)How you will block pron sites using Squid proxy?

    7)Give me details how to configure mail support for NAGIOS?

    8)Can you use NAGIOS to send SMS? how to do that?

    9)What is web-min?
    A) Webmin is a web-based system configuration tool for OpenSolaris, Linux and other Unix-like systems.

    10)How you will do kernel compilation? Explain each step?

    11)What is the difference between SGID, SUID and sticky bit?

    12)How to restrict users to set password with complexity ?

    13)How do you monitor system performance?

    14)Which are the configuration files of FTP server?

    15)What are the different types of FTP servers?

    16)What is the difference between active FTP and passive FTP?

    17)How you will configure FTP in DMZ?

    18)What is the use of htaccess file?

    19)how do you configure website authentication for user logins?

    20)Give me the steps to configure sendmail.

    21)How to block particular network not to access my sendmail server?

    22)How to send duplex/half duplex etc to the network card?

    23)Can a web server have multiple ip add? if yes why? if no why?

    24)How to configure multiple ip address for a web server?

    25)What is the difference between VMWare and XEN?

    26)Explain me the difference between ext2 and ext3

    27)How do you configure route in Linux server?

    28)How do you make routes permanent in Linux server?

    29)Why you want to change your job?

    30)What is an inode?

    31)what is the difference between soft link and hard link?

    32)How to get info about the files which are not accessed from last 30days?

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