The umask command

Before you do anything on a new production server or any machine where the web server process runs as another user than you, we recommend to configure your umask correctly.

When a process with a too restrictive umask runs some code of a repository with Python source files, it will create .pyc files. And when you later try to upgrade that repository, you get questions of style:

rm: remove write-protected regular file `./lino_noi/lib/noi/roles.pyc'?

The same is valid for other files created by some process: log files, snapshots, ...

The default umask on most systems is 022, which causes any new files created by a process to not be writable for other group members.

A umask 002 makes sure that every user running a Python process in this environment will create new files so that they are writable for other group members.

The umask is used to mask (disable) certain file permissions from any new file created by a given user. All system users on a Lino site should have a umask 002 or 007 (not 022 or 077 as is the default value).

How to configure umask

  • Maintainers : Edit either the file ~/.bashrc of each system user or the file /etc/bash.bashrc (site-wide for all users) and add the following line at the end:

    umask 002
    
  • Apache : Add one line to your /etc/apache2/envvars file:

    umask 002
    
  • Supervisor : set username = www-data in your job confiruation files

  • cron : when calling a task from cron.daily the user is cron, so we must set umask in every process. When calling tasks from a crontab, we can set the user to www-data there.

More about umask

The umask is a group of bits which specifies which permissions are to be masked (not given) when a given user creates a new file.

For example an octal umask value of 022 (000 010 010 in binary) means that the permissions "group write" and "others write" will be masked (not set) on new files. If you change 022 to 002 (or 007), then the group write will be set. Here is an illustrative table:

===== ===== ===== =====
umask user  group other
===== ===== ===== =====
      R W X R W X R W X
----- ----- ----- -----
022   - - - - 1 - - 1 -
002   - - - - - - - 1 -
007   - - - - - - 1 1 1
===== ===== ===== =====