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October 20, 2018

Linux/UNIX Interview Questions/FAQs for Oracle DBAs

UNIX/Linux/Solaris Interview Questions for Oracle DBAs

1. What’s the difference between soft link and hard link?
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?

while read line
echo $line
done < file_name

3. What’s the use of umask?

Will decide the default permissions for files.

4. What is the default value of umask?


5. What is crontab and what are the arguments?

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)

6. How to find operating system (OS) version?
uname –a

7. How to find out the run level of the user?
uname –r

8. What is load average ?

Load Average is the value which represents the load on the system for a specific period of time. Also it can be considered the ratio of the number of active tasks to the number of available CPUs.
run queue length - the sum of the number of processes that are currently running plus the number that are waiting (queued) to run.

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

10. How to delete 7 days old trace files?

find ./trace –name *.trc –mtime +7 –exec rm {} \;

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

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

13. What is paging?

14. What  are huge pages?

15. How to find out the status of last command executed?

16. How to find out number of arguments passed to a shell script?


17. How to add user in Solaris/Linux?
useradd command

18. What does sudo stand for in Linux systems?
Abbreviation of sudo is "substitute user do" (some people will abbreviate it as "super user do"), which allows users to run programs with the security privileges of another user, by default the superuser.

19. How to find out memory size of Linux host?

20. How to find out number CPUs in Linux host?

Related Oracle DBA Interview Articles: Oracle Exadata Interview Questions/FAQs   Oracle Data Guard Interview Questions/FAQs  Oracle DBA RAC Interview Questions/FAQs


  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
    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
    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


    Irene Hynes

  2. Please try:

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

  3. Nice blog. Thanks for sharing this information. Keep updating.....
    Linux Online Training

  4. Uname -r will print only the kernel release version?
    runlevel command will only print the current run level.