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howto:umask [2019/03/07 17:11]
wikiadmin created
howto:umask [2019/03/07 17:47] (current)
wikiadmin
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 ======umask====== ======umask======
  
-The CHPC cluster uses CentOS as its operating system and follows the user private group scheme ​for user accounts. This means that each user has a username (UID) and a corresponding group (GID). ​ This scheme allows for easier set up of shared directories on the various file systems (home or Lustre) that users have access to.+The CHPC cluster uses CentOS as its operating system and follows the user private group convention ​for user accounts. This means that each user has a username (UID) and a corresponding group (GID). ​ This scheme allows for easier set up of shared directories on the various file systems (home or Lustre) that users have access to. 
 + 
 +=====Default umask===== 
 + 
 +The default umask is set by the ''​umask''​ command in your ''​.bashrc''​ or the system wide ''/​etc/​bashrc''​ file.  For RedHat derived systems (CentOS) the default umask is ''​002''​ which means the the group permissions of your files and directories will match the user permissions and include write access, the ''​w''​ flag. 
 + 
 +This is needed for shared groups (not your private user group) where all members of the group need write access. 
 + 
 +=====Checking your current umask===== 
 + 
 +Simply run the command ''​umask''​ without any arguments on the shell: 
 + 
 +  umask 
 + 
 +and your current umask setting will be displayed:​ 
 + 
 +  002 
 + 
 +To change it, run the umask command with the desired umask as the sole argument: 
 + 
 +  umask 022 
 + 
 +And you can confirm this by running ''​umask''​ on its own again. 
 + 
 +=====CHPC Standard===== 
 + 
 +The CHPC departs from the user private convention in one important way.  The convention would normally only specify that the user is a member of the user's private group. ​ The CHPC adds the user name of the CHPC staff member responsible for supporting your programme. 
 + 
 +So, instead of 
 + 
 +  auser:​*:​555:​ 
 + 
 +where there is no user in the group, we have 
 + 
 +  auser:​*:​555:​chpcstaff 
 + 
 +where ''​chpcstaff''​ would be the username of the CHPC staff member. 
 + 
 +This is to allow our staff to have access to your files to help you with technical issues. 
 + 
 +=====Disabling write access===== 
 + 
 +If you want to remove the ''​w''​ access from the group permission you will need to change your umask and also change all the current permission bits. 
 + 
 +====Step 1: umask==== 
 + 
 +Edit your ''​.bashrc''​ file in you home directory and add the line 
 + 
 +  umask 0022 
 + 
 +at the end of the file.  Save it.  Now when you log in next time your umask will block ''​w''​ from group access. 
 + 
 + 
 +====Step 2: remove w access from all files and directories==== 
 + 
 +Warning: this can take a long time if you have a lot of files so first launch an interactive session before running these commands. 
 + 
 +  qsub -I 
 +   
 +Use the ''​find''​ command: 
 + 
 +  find . -exec chmod g-w \{\} \; 
  
  
/var/www/wiki/data/pages/howto/umask.txt · Last modified: 2019/03/07 17:47 by wikiadmin