File Systems and Permissions Summary

 

1. chmod -rwxr-xr-1 instruct staff 270311 Aug 11 2009 install.sh

I will attempt explain the best I can.

Chmod, on linux or unix like operating systems, there are a set of rules for each file which defines who can access that file and how they can access it. The ‘ – ‘ at position               0 denotes the type of file, it is either a ‘ d ‘ if the item  is a directory               or ‘ l ‘ if it is a link or               it could just be a regular file. The symbols in the positions 1 thru 3               ‘ rwr ‘ are               permissions for the owner of the file and the symbols in position 4 thru 6 ‘ r-x ‘ are               positions for a group, the remaining positions 7 thru 9 ‘ r-1 ‘ are permissions for               anyone else. The rwx shows that owner has read (r), write (w) and execute (x)               permission. The shows the permissions for the group to which the file belongs. The

r-xr– represents that  has permission to read (r) and execute (x) and, read permissions               without write permission. The last xr-1 set of  characters, represents the               permissions               for everybody else. The octal numbers 270311 each have individual               meanings for permissions. I researched this at, the WEB site below on the reference               page. Now, 2 is for write, the 7 where my confusion stepped in is the numeric mode               from one to four octal digits which are derived by adding up the bit values, so 4 is for               read , 2 for write, and 1 is for execute when added equals 7 so all access is allowed.               The 0 from what I read has no permissions. The 3 is for write and execute and the 1’s               only can execute. How the commands and the octal numbers relate requires me to do               more homework. The remaining items  below 2 -5 and 1 – 4, will be described and               follow the same patterns as above. I just hope I’m explaining things correctly.

2. Chmod -rw-r–r–1 instruct staff 348039 Aug 12 2008 User_Guide.txt

Chmod, on linux or unix like operating systems, there are a set of rules for each file which defines who can access that file and how they can access it. The ‘ – ‘ at position               0 denotes the type of file, it is either a ‘ d ‘ if the item  is a directory               or ‘ l ‘ if it is a link or               it could just be a regular file. The symbols in the positions 1 thru 3               ‘ rw- ‘ are               permissions for the owner of the file and the symbols in position 4 thru 6 ‘ r– ‘ are               positions for a group, the remaining positions 7 thru 10 ‘ r–1 ‘ are permissions for               anyone else. Now, this textual representation consist of 10 characters but from what I have read the rules still apply. The octal numbers 348039 each again have individual               meanings for permissions. Now, 3 is for write, the 4 is for read, 8 again confusion stepped in until I will research this more. The 0 is for denial, 3 again is for write and of course there is a 9 I’ll also have to look into.

3. Chmod -rw-r—–1 instruct staff 635106 Aug 12 2009 Admin_Guide.txt

Chmod, on linux or unix like operating systems, there are a set of rules for each file which defines who can access that file and how they can access it. The ‘ – ‘ at position               0 denotes the type of file, it is either a ‘ d ‘ if the item  is a directory               or ‘ l ‘ if it is a link or               it could just be a regular file. The symbols in the positions 1 thru 3               ‘ rw- ‘ are               permissions for the owner of the file and the symbols in position 4 thru 6 ‘ r– ‘ are               positions for a group, the remaining positions 7 thru 10 ‘ —1 ‘ are permissions for               anyone else. Now, this textual representation consist of 10 characters but from what I have read the rules still apply. The octal numbers 635106 each again have individual               meanings for permissions. Now, 6 is for read/write, the 3 is for write, 5 is for  read/execute. The 1 is for execute only, 0 all access denied and 6 read/write.

4. Chmod drwxr-xr-x 4 instruct staff 144 Aug 12 2009 Documents

Chmod, on linux or unix like operating systems, there are a set of rules for each file which defines who can access that file and how they can access it. The ‘ d ‘ at position 0 denotes the type of file, it is either a ‘ d ‘ if the item  is a directory               or ‘ l ‘ if it is a link or it could just be a regular file. Well this is a directory. The symbols in the positions 1 thru 3 ‘ rwx ‘ are permissions for the owner of the file and the symbols in position 4 thru 6

‘ -x4 ‘ are positions for a group. The octal numbers 144 each again have individual meanings for permissions. Now, 1 is for execute only. The two 4’s are read only access.

5. chmod -rwsr-x 1 nobody nobody 169202 Aug 11 2009 httpd

 Chmod, on linux or unix like operating systems, there are a set of rules for each file which defines who can access that file and how they can access it. The ‘ – ‘ at position 0 denotes the type of file, it is either a ‘ d ‘ if the item  is a directory               or ‘ l ‘ if it is a link or it could just be a regular file. The symbols in the positions 1 thru 3 ‘ rws ‘ are permissions for the owner of the file and the symbols in position 4 thru 7

‘ r-x1 ‘ are positions for a group. The octal numbers 169202 each again have individual meanings for permissions. Now, 1 is for execute only. The 6 is for read/write allowed, the 9 I still have not figured out yet, but I will. The 2 is for write access only, the 0 means all access denied, again the 2 is write access only.

Metacharacters/Regular Expressions

1.               * Matches zero or more occurrences of the previous character
2.               ? The preceding item is optional and will be matched, at most, once.
3.               ^ The caret “^” is an anchor that indicates the beginning of a line.
4.               $ The asterisk is a modifier and also an anchor. In a regular expression it specifies that a previous character set can appear any number of times,                that includes a zero.
5.               [0-9] Matches any one of the numbers given within chars, where chars Is a sequence of characters.
6.           [a-z]  Matches any one of the characters given within chars, where chars Is a sequence of characters.

Regular expressions to match the following

1. All files that end in txt

ls -1 grep ‘*.txt’

2. Files that have a second character of a and end in sh

ls -1 | grep ‘*.sh’

3. Any file that starts with a number
4. ls -l | grep ‘[0-9]’
5. A blank line

ls -l | grep ‘[]’

6. A traditional 10-digit U.S.-based phone number, in the following format:

(407) 555-1212

ls -l | grep ‘[(0-3)] [0-3]-[0-4]’   Note: Not quite sure about this one but I tried.

 

Reference

www.computerhope.com/unix/uchmod.htm