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October 20, 2012

UNIX Interview Questions/FAQs for Oracle DBAs

UNIX Interview Questions/FAQs for Oracle DBAs


1. What’s the difference between soft link and hard link?
Ans:
A symbolic (soft) linked file and the targeted file can be located on the same or different file system while for a hard link they must be located on the same file system, because they share same inode number and an inode table is unique to a file system, both must be on the same file system.

2. How you will read a file from shell script?
Ans:
while read line
do
echo $line
done < file_name

3. What’s the use of umask?
Ans:
Will decide the default permissions for files.

4. What is crontab and what are the arguments?
Ans:
The entries have the following elements:
field             allowed values
-----             --------------
minute            0-59
hour                0-23
day of month   1-31
month             1-12
day of week     0-7 (both 0 and 7 are Sunday)
user                 Valid OS user
command         Valid command or script

? ? ? ? ? command
|  | |  | |_________day of the week (0-6, 0=Sunday)
|  | |  |___________month (1-12)
|  | |_____________day of the month (1-31)
|  |_______________hour (0-23)
|_________________minute (0-59)


5. How to find operating system (OS) version?
Ans:
uname –a


6. How to find out the run level of the user?
Ans:
uname –r

7. How to delete 7 days old trace files?
Ans:
find ./trace –name *.trc –mtime +7 –exec rm {} \;

8. How to get 10th line of a file (by using grep)?

9. (In Solaris) how to find out whether it’s 32bit or 64bit?

10. What is paging?


11. What is top command?
Ans:
top is a operating system command, it will display top processes which are taking high cpu and memory.

12. How to find out the status of last command executed?
Ans:
$?

13. How to find out number of arguments passed to a shell script?
Ans:
$#

14. What is the default value of umask?
Ans:
022


15. How to add user in Solaris/Linux?
Ans:
useradd command


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2 comments:

  1. Hi There,
    . I'm trying to find a SQL-statement for what's in column "Occurences" below. I need to calculate the amount of times a "User" has a "Filename" with similar name (regardless the Drive and Folder it is stored).
    The output of below query is not correct. I want to get those MEMID which has more than one DOB records rows.
    create table #Mem (MEMID varchar(20), DOB datetime, MEMRef varchar(20), MEMLogdate datetime)
    insert into #Mem values ('4651','1956-12-19','A','1989-05-29')
    insert into #Mem values ('1233','1956-12-19','A','2011-07-07')
    insert into #Mem values ('1233','1956-12-19','A','1997-09-08')

    insert into #Mem values ('1235','1957-12-19','A','2012-07-07')
    insert into #Mem values ('1235','1957-12-19','A','1998-09-08')

    insert into #Mem values ('1236','1959-12-19','A','1998-09-08')
    ;with duplicateDOB as (
    select dob from #Mem group by dob having count(*) > 1
    )
    select * from #Mem
    where dob in (select * from duplicateDOB)

    --Current Output
    MEMID DOB MEMRef MEMLogdate
    4651 1956-12-19
    A 1989-05-29 --This row should not be in output because this has only one row
    1233 1956-12-19
    A 2011-07-07
    1233 1956-12-19
    A 1997-09-08
    1235 1957-12-19
    A 2012-07-07
    1235 1957-12-19
    A 1998-09-08

    --Desired Output
    MEMID DOB
    MEMRef MEMLogdate
    1233 1956-12-19
    A 2011-07-07
    1233 1956-12-19
    A 1997-09-08
    1235 1957-12-19
    A 2012-07-07
    1235 1957-12-19
    A 1998-09-08

    Regards,

    Irene Hynes

    ReplyDelete
  2. Please try:

    select MEMID, DOB from #Mem group by MEMID,DOB having count(*) >1;

    ReplyDelete