CPSCI 107: Applications, Implications, and Issues

Lab 12

April 19, 2006

Collaborating using Unix Groups

Today's Topics

This is a list of the topics we'll discuss today (more or less, time permitting).

• Reading the ls -l directory listing
• The Linux User Private Group (UPG) scheme
• Determining what groups you're a member of: groups
• Granting group access to a directory: chmod. Suggestions:
  • do this only in a directory created expressly for this purpose
  • if the directory is in your public_html tree, you know that all parent directories are o+x
  • if you don't want the contents available outside the group, you can set the directory o-r and the individual files o-rwx
• Setting the group who can access a file: chgrp
• Changing your current primary group: newgrp
• Setting group permissions on a directory: chmod
• Setting group permissions on a file: chmod
• Setting things so that newly-created files inherit the group membership of the directory: chmod +s
• Only the file owner can chmod a file!
• Setting the “sticky bit” on a directory: chmod +t
• How umask (set in your .bashrc file) works
• The UPG scheme and appropriate settings for umask 
  • Not all Unix/Linux systems use the UPG scheme! On those systems, you might want to rethink the umask settings. On warp, we are using UPG.

Today's Assignment

Go to the ctc webspace and modify the dl element in index.html to include your name as the content of a dt element and a few sentences about yourself as the content of the corresponding dd element.

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