Q) Which command will list only sub – directories ?

Ans - $ ls –ld<Enter – Key>

Some Special Listings: -

Q) How to list the sub – directories which has 3 characters in first three letter and then p ?

Ans - $ ls ???p<Enter – Key>

Q) How to long list the sub – directories which has any one vowel in first letter , then one character and then anything ?

Ans - $ ls –l [aeiouAEIOU]?*<Enter – Key>

Q) How to list the sub – directories which has ‘h’ in first letter, then a character in 2^nd letter, and then ‘ran’ ?

Ans - $ ls h?ran<Enter – Key>

Q) How to list the sub – directories which have 5 characters where as 1^st character may be from ‘a’ to ‘k’, 2^nd character may be from ‘d’ to ‘s’, 3^rd character may be a number from ‘0’ to ‘9’ and then two valid characters ?

Ans - $ ls [a-k][d-s][0-9]??<Enter – Key>

Permission and its change: -

Q) What is the base permission of file and directory ?

Ans – Base permission of file – 666 and directory – 777.

Q) What is umask and its default value ?

Ans – Unmask is the value which determine the default file or directory permission during its creation.

Its default value is 022.

Q) What is the default permission of file and directory ?

Ans – Default permission of file is 644 and directory is 755.

Q) Which command is use to change the permission of file or directory ?

Ans – chmod

Where chmod -> change mode

Q) What is absolute and relative permission ?

Ans – Absolute permission is related to numerical value.

Read – 4

Write – 2

Execute – 1

Relative Permission is related to symbolic value.

Read – r

Write – w

Execute – x

i.e. owner has read, write and execute permission(rwx)(4+2+1).

Group has read and execute permission(r-x)(4+0+1).

Others has execute permission on the same directory(--x)(0+0+1).

Then the absolute permission will be 751.

Then the relative permission will be rwxr-x—x.

Q) Write a command to change the permission of a file f.txt to a new permission 611 ?

Ans - $ chmod 611 f.txt<Enter – Key>

Q) Write a command to change the permission of a directory d1 to a new permission 742 ?

Ans - $ chmod 742 d1<Enter – Key>

Q) Write a command to give owner/user and other read and execute permission for a file f12.dat ?

Ans - $ chmod uo+rx f12.dat<Enter – Key>

Q) Write a command to take back execute permission from group and other and give read permission to other for a directory d1 ?

Ans - $ chmod go-x,o+r d1<Enter – Key>

Q) Write a command which replaces all existing permission for a file file.csv to read write for all ?

Ans - $ chmod ugo=rw file.csv<Enter – Key>

Q) Write a command to give read permission to all for a directory d3 ?

Ans - $ chmod +r d3<Enter – Key>

Q) Write a command which replaces all permission of group and other to read and user to read and write for a directory d456 ?

Ans - $ chmod go=r,u=rw d456<Enter – Key>