date: mon 18/03/1432

1Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

Date: MON 18/03/1432

Lecture 1

Security & permissions commands

Umask(User Mask

Umask abbreviation of user maskIs a command to set the file mode creation

mask(Umask) sets the file-creation permissions

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Umask(User Mask

Symbolic mask:Umask -Sdisplays the existing default value for new filesFor example the result of the last command may be

like:u=rwx,g=rwx,o=rx

This means creating new files with the mode:-rw-rw-r--

And directories with the mode:Drwxrwxr- x

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Umask(User Mask

Notes:r:readw:writeX:excuteu:userg:groupo:other r=4w=2x=1

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Umask(User Mask

Octal mask:• 666 in the case of files,• 777 in the case of directories.• The octal notation is as follows:• 0 – read, write and execute • 1 – read and write• 2 – read and execute• 3 – read only • 4 – write and execute • 5 – write only • 6 – execute only • 7 – no permissions

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Umask(User Mask

(Umask 022)causes files to be created with permissions of 644

(rw-r--r--) ,and directories to be created with permissions of

755 (rwxr-xr-x

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Umask(User Mask

022 (masking out the write permission for the group and others), which ensures that new files are only writable for the owner (i.e. the user who created them).

Another common value is 002, which leaves the write permission for the file's group enabled. This can be used for files in shared workspaces, where several users work with the same files

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Umask(User Mask

umask 0174 mkdir footouch bar ls -l drw-----wx 2 dave dave 512 Sep 1 20:59 foo -rw----w- 1 dave dave 0 Sep 1 20:59 bar

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chmod (change mode)

(chmod) set permissions (modes) of files or directories

Chmod +rwx file-nameTo add read write and execute for all

Chmod -rwx file-nameTo remove read write and execute from all

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chmod (change mode)

Change mode of MYFILE to -rw-rw-r--chmod 664 myfile ls -l myfile -rw-rw-r-- 1 57 Jul 3 10:13 myfile

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chmod (change mode)

• Add the read and write permissions to the user and group classes of a directory:

chmod ug+rw mydir ls -ld mydir drw-rw---- 2 unixguy uguys 96 Dec 8 12:53 mydir

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chmod (change mode)

remove write permissions for all classes:chmod a-w myfile ls -l myfile -r-xr-xr-x 2 unixguy uguys 96 Dec 8 12:53 myfile

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chmod (change mode)

Set the permissions for the user and the group to read and execute only (no write permission) on mydir:

chmod ug=rx mydir ls -ld mydir dr-xr-x--- 2 unixguy uguys 96 Dec 8 12:53 mydir

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chgrp(change group)

(chgrp) changes group associated with file. chgrp group files

Orchgrp -R group files .

Note:Can be used to change the group associated with

subdirectories and files of a directory.

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chgrp(change group)

ls -l fu-rw-r--r-- 1 amani amani 545 Nov 04 2004 fuchgrp work fuls -l fu-rw-r--r-- 1 amani work 545 Nov 04 2004 fu

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chown(change owner)

• chown - changes ownership of a file. (chown userid files )

or: • chown -R userid files

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chown(change owner)

chown root fuls –l fu-rwxrwx--- 1 root work 0 Sep 27 19:30 fu

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End

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