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Lecture 1. Security & permissions commands. Date: MON 18/03/1432. Umask(U ser Mask. Umask abbreviation of u ser mask Is a command to set the file mode creation mask ( Umask ) sets the file-creation permissions. Umask(U ser Mask. Symbolic mask: Umask -S

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slide1

Lecture 1

Security & permissions commands

Date: MON 18/03/1432

Ustaza. Imtithal Alnour Saeed & UstazaSana AL-Hwishel

slide2

Umask(User Mask

  • Umask abbreviation of user mask
  • Is a command to set the file mode creation mask
  • (Umask) sets the file-creation permissions

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

slide3

Umask(User Mask

Symbolic mask:

Umask -S

  • displays the existing default value for new files
  • For 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

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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Umask(User Mask

Notes:

r:read

w:write

X:excute

u:user

g:group

o:other

  • r=4
  • w=2
  • x=1

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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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

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

slide6

Umask(User Mask

(Umask022)

  • causes files to be created with permissions of 644 (rw-r--r--) ,
  • and directories to be created with permissions of 755 (rwxr-xr-x

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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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

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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Umask(User Mask

umask 0174

mkdir foo

touch 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

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

slide9

chmod (change mode)

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

Chmod +rwx file-name

To add read write and execute for all

Chmod -rwx file-name

To remove read write and execute from all

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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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

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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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

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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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

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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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

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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chgrp(change group)

  • (chgrp) changes group associated with file.

chgrpgroupfiles

Or

chgrp -R group files .

Note:

Can be used to change the group associated with subdirectories and files of a directory.

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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chgrp(change group)

ls -l fu

-rw-r--r-- 1 amani amani 545 Nov 04 2004 fu

chgrp workfu

ls -l fu

-rw-r--r-- 1 amani work 545 Nov 04 2004 fu

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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chown(change owner)

  • chown - changes ownership of a file.

(chown userid files )

or:

  • chown -R userid files

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

slide17

chown(change owner)

chown root fu

ls –l fu

-rwxrwx--- 1 root work 0 Sep 27 19:30 fu

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

slide18

End

Ustaza. Imtithal Alnour Saeed & Ustaza Sana AL-Hwishel

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