Chapter 3 Some additional notes… File permissions A file has three types of permissions (read, write and execute). Available to three categories of users (user, group and others). Can see the permission settings using ls –l {apache:~/public_html/CS3375} ls -l total rw-r--r-- 1 kkhan cs 3961 Jan 29 20: html -rw-r--r-- 1 kkhan cs Jan 21 03:11 Syllabus_3375_sp08.doc -rw-r--r-- 1 kkhan cs Jan 7 13:27 Your_UNIX_2e.ppt - r-x The total line tells how many blocks (usually 1024 bytes per block) are contained in this directory. Directory, followed by three sets of 3 bits indicating permissions First set? Owner Second set? Group Third set? Others r stands for read, w stands for write, x stands for execute Owner can read and execute this file

Chapter 3 Some additional notes… Copying Permissions As one other shortcut, it’s possible to tell chmod “give users of one class the same permissions that some other class has.” Let’s say we have these files: d------rwx joe acctg sales -rw-r--r-- joe acctg info.dat The other users have full permissions on the sales directory. We’d like to say “ the user and group should be assigned (=) the permissions belonging to others.” That translates to: chmod ug=o Similarly, to make info.dat readable and writable to the group, we can say: chmod g=u info.dat (you can read this as “the group is assigned (=) the permissions currently held by the user.”) You may also use + and - to add and subtract the permissions that currently belong to a different class of user. You can’t mix the standard permissions (r, w, and x) with the coyping shortcuts. chmod will protest if you give it something like this: chmod g=wu info.dat

Need to be able to change the file permissions Why? –Protect files from accidental deletion or modification (archive) –Allow team members to read, modify, execute, possibly even delete a file without having to send them a copy –Setting up your webpage on unix – have to make the html files accessible or no one will be able to see it! –… Unix command is chmod –Command allows us to change the permission settings Examples (can use relative or absolute permissions): chmod o+rwx testfile1 -r-x---rwx 1 kkhan cs 24 Sep 7 10:41 testfile1 // “o” is for “other”, “+” means add permission

Need to be able to change the file permissions Examples cont. Change it back? chmod o-rwx testfile1 Results in: -r-x kkhan cs 24 Sep 7 10:41 testfile1 // “-” means remove permission Can also use absolute (binary) mode chmod 507 testfile1 Results in: -r-x---rwx 1 kkhan cs 24 Sep 7 10:41 testfile r-x rwx (Bits are set or cleared)

Need to be able to change the file permissions Access to files is not independent of the permissions on the directories The directory is the “parent”; permissions on the parent cannot be over-ridden by permissions on its files Examples Directory is set with no write access –Cannot add or delete a file in the directory no matter what its permissions are Question: could we edit a file in this directory? –Only if we have write permission for the file Directory is set with no read or execute access –Question: could we run an html file in this directory? –No (this is a common problem setting up webpages)

Need to be able to change the file permissions Man chmod chmod [-fR] absolute-mode file... chmod [-fR] symbolic-mode-list file... -f Force. chmod will not complain if it fails to change the mode of a file. -R Recursively descends through directory arguments, setting the mode for each file as described above. Problem: I’m building my website and I want to set all my files in the directory public_html so everyone can read and execute my html file chmod –R a+rx public_html Review: chmod Solves Problems

File Permission Exercise Set the permissions as follows: testdir1 group & other has no access testfile1.html group & other has no access testfile2.html group & other has read access testfile3.html group & other has write access testfile4.html group & other has execute access testfile5.html group & other has read and execute access testfile6.html group & other has read and write access testfile7.html group & other has write and execute access testfile8.html group & other has read, write, and execute access

File Permission Exercise testdir2 group & other has read access // 8 files testdir3 group & other has write access // 8 files testdir4 group & other has execute access // 8 files testdir5 group & other has read and execute access // 8 files testdir6 group & other has read and write access // 8 files testdir7 group & other has write and execute access // 8 files testdir8 group & other has read, write, and execute access

File Permission Exercise Now, try to: display the contents of each directory e.g., ls testdir1 display a long listing of each directory e.g., ls –l testdir1 why don’t these two list commands behave the same way? display the contents of each file in each subdirectory e.g., more testfile1.html change the contents of each file e.g., echo “trying to change the file” >> testfile1.html delete each file e.g., rm testfile1.html

File Permission Exercise To test the ability to load a.html file in a browser, you need to set up a softlink (aka symbolic link) under your public_html directory cd cd public_html ln -s - creates a softlink (called link name), which points to the original subdirectory e.g., ln –s ~kkhan/public_html/testfiles testdir cd takes you to the original subdirectory cd testdir Now, in the browser (for example running on the pc) you can use the open file option to test loading the.html files If the file loaded successfully, then there is a brief text displayed from the file Try loading one that definitely should work: testdir8/testfile8.html