Unix/Linux administration interview questions

What is LILO?

LILO stands for Linux boot loader. It will load the MBR, master boot record, into the memory, and tell the system which partition and hard drive to boot from.

What is the main advantage of creating links to a file instead of copies of the file?

A: The main advantage is not really that it saves disk space (though it does that too) but, rather, that a change of permissions on the file is applied to all the link access points. The link will show permissions of lrwxrwxrwx but that is for the link itself and not the access to the file to which the link points. Thus if you want to change the permissions for a command, such as su, you only have to do it on the original. With copies you have to find all of the copies and change permission on each of the copies.

Write a command to find all of the files which have been accessed within the last 30 days.

find / -type f -atime -30 > December.files

This command will find all the files under root, which is ‘/’, with file type is file. ‘-atime -30′ will give all the files accessed less than 30 days ago. And the output will put into a file call December.files.

What is the most graceful way to get to run level single user mode?

A: The most graceful way is to use the command init s.
If you want to shut everything down before going to single user mode then do init 0 first and from the ok prompt do a boot -s.

What does the following command line produce? Explain each aspect of this line.

$ (date ; ps -ef | awk ‘{print $1}’ | sort | uniq | wc -l ) >> Activity.log

A: First let’s dissect the line: The date gives the date and time as the first command of the line, this is followed by the a list of all running processes in long form with UIDs listed first, this is the ps -ef. These are fed into the awk which filters out all but the UIDs; these UIDs are piped into sort for no discernible reason and then onto uniq (now we see the reason for the sort - uniq only works on sorted data - if the list is A, B, A, then A, B, A will be the output of uniq, but if it’s A, A, B then A, B is the output) which produces only one copy of each UID.

These UIDs are fed into wc -l which counts the lines - in this case the number of distinct UIDs running processes on the system. Finally the results of these two commands, the date and the wc -l, are appended to the file "Activity.log". Now to answer the question as to what this command line produces. This writes the date and time into the file Activity.log together with the number of distinct users who have processes running on the system at that time. If the file already exists, then these items are appended to the file, otherwise the file is created.

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6 Comments on Unix/Linux administration interview questions

  1. George Swan
    Posted 1/27/2004 at 7:47 am | Permalink

    The last question in your “Unix/Linux administration interview questions” is missing a character. You have awk execute a program from the command line. You have a trailing quote, because this program must be a single argument. But the opening quote is missing. The pipeline in your example won’t work.

  2. Rohit Raj
    Posted 2/12/2004 at 11:02 pm | Permalink

    This is one of the best site to lern and get idea if information, this is useful also, my all friend yse this only,

  3. .
    Posted 5/1/2007 at 4:08 pm | Permalink

    The syntax does work:

    date; ps -ef | awk ‘{ print $1 }’ | sort | uniq | wc -l

  4. Gopinath
    Posted 6/28/2008 at 7:22 am | Permalink

    date; ps -ef | awk ‘{ print $1 }’ | sort | uniq | wc -l
    It work really.. just check it out

  5. Rory Browne
    Posted 8/21/2008 at 5:16 pm | Permalink

    Question 4 is slightly misleading.

    Is the $ part of the prompt, or part of the command.

    First time I looked at it I thought it would produce an error message something along the lines of Thu: command not found, but when I look at it again, assuming the $ to be the prompt, then it’s fairly clear that the brackets produce a sub-shell, and sends the output of the commands in question to the file in question.

    It is a rather bad command however, since it’s not really the best way to get this information, and would also count people who aren’t logged in, but may be running scheduled ( aka cron ) jobs.

  6. Posted 1/8/2009 at 3:52 am | Permalink

    date; ps -ef | awk ‘{ print $1 }’ | sort | uniq | wc -l

    do not copy paste from web and it will work
    ‘{ print $1 }’ –must be type by hand

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