Changing File Permissions Using Unix Commands

The following
information will help you to use Unix commands to change file permissions.
If you have not already done so, you may want to review the document Unix
File Permissions
. Please note that Unix can be a very user-unfriendly
environment. For a start-to-finish tutorial on working in the Unix environment,
please see Unix for Web Designers.

Directions
for:

Single-user
sites

The steps
for correcting permissions errors on single-user sites are as follows:

  1. establish
    a secure connection (using SecureCRT or NiftyTelnet – both are available
    from Software Central) to the server
    which houses your web pages
  2. issue
    the Unix command chmod for any files or directories which need
    to be changed.
Scenario:
User mst3k is getting a permissions error when trying to view his
web site at http://www.people.virginia.edu/~mst3k.

After
logging into blue.unix.virginia.edu with SecureCRT, mst3k issues
the following on the Unix command line:

cd public_html

to go to
the directory where his web page is stored. He then views the permissions
by issuing the command:

ls -l
home.html

and sees
the following output:

-rw-r—–
1 mst3k staff 724 Jan 17 2001 home.html

Permissions
are organized into three major groupings. In this example the permissions
for user are rw-, the permissions for group
are r–, and the permissions for other are .

This file
is not viewable on the web because “other” does not have
read permissions. To correct the problem, mst3k issues the command:

chmod
o+r home.html

To verify
that the command produced the desired results, mst3k again issues the
command:

ls -l
home.html

and sees
the following output:

-rw-r–r–
1 mst3k staff 724 Jan 17 2001 home.html

Provided
that the permissions of the parent directories are correct, the
page should now be viewable on the web.

The following
chart outlines the recommended permission settings for the files and directories
in single-user web sites:

Recommended
Permissions for single-user web sites

File
Permissions

User

Group

Other

read

read

read

write

rw-r–r–

 

Directory
Permissions

User

Group

Other

read

write

execute

execute

execute

rwx–x–x


Group-maintained
sites

The steps
for correcting permissions errors on group-maintained sites are as follows:

  1. establish
    a secure connection (using SecureCRT or NiftyTelnet – both are available
    from Software Central) to the server
    which houses your web pages
  2. Verify
    that the group ownership of your files is correct
  3. issue
    the Unix command chmod for any files or directories which need
    to be changed.
Scenario:
User mst3k is getting a permissions error when trying to edit the
file home.html in the group-maintained site http://www.virginia.edu/somesite

After
logging into minerva.acc.virginia.edu with SecureCRT, mst3k issues
the following on the Unix command line:

cd
/www/doc/somesite

to
go to the directory where the web page is stored. He then views
the permissions by issuing the command:

ls
-l home.html

and
sees the following output:

-rw-r–r–
1 abc2d staff 724 Jan 17 2001 home.html

There
are two problems with this file: (1) The group ownership
is not correct; (2) group write permissions have not been
set.

To
correct this problem, mst3k goes to find the owner of the file –
abc2d. Only the owner of the file may change the group ownership
or permissions.

abc2d
then logs into her account and repeats the steps above. To change
the group ownership, she issues the command:

chgrp
somegrp home.html

where
somegrp is the group that was designated for this web site.
She then adds group write permissions by issuing the command:

chmod
g+w home.html

Finally,
she verifies that the changes were made by issuing the command:

ls
-l home.html

and
sees the following output:

-rw-rw-r–
1 abc2d somegrp 724 Jan 17 2001 home.html

Provided
that mst3k is a member of the group somegrp, he will now be able
to edit the file.

The following
chart outlines the recommended permission settings for the files and directories
in group-maintained web sites:

Recommended
Permissions for group-maintained web sites

File
Permissions

User

Group

Other

read

read

read

write

write

rw-rw-r

 

Directory
Permissions

User

Group

Other

read

read

write

write

execute

execute

execute

rwxrwx–x

Leave a Reply