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GNU cfengine

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4.3 Files and links

File and link management takes several forms. Actions are divided into three categories called files, tidy and links. The first of these is used to check the existence of, the ownership and permissions of files. The second concerns the systematic deletion of garbage files. The third is a link manager which tests, makes and destroys links. The monitoring of file access bits and ownership can be set up for individual files and for directory trees, with controlled recursion. Files which do not meet the specified criteria can be `fixed' --i.e. automatically set to the correct permissions, or can simply be brought to the attention of the system administrator by a warning. The syntax of such a command is as follows:

 
files:

  class::

    /path mode=mode owner=owner group=group

         recurse=no-of-levels action=action

The directory or file name is the point at which cfagent begins looking for files. From this point the search for files proceeds recursively into subdirectories with a maximum limit set by the recurse directive, and various options for dealing with symbolic links and device boundaries. The mode-string defines the allowed file-mode (by analogy with `chmod') and the owner and group may specify lists of acceptable user-ids and group-ids. The action taken in response to a file which does not meet acceptable criteria is specified in the action directive. It includes warning about or directly fixing all files, or plain files or directories only. Safe defaults exist for these directives so that in practice they may be treated as options.

For example,
 
files:

  any::
       /usr/*/bin mode=a+rx,o-w own=root r=inf act=fixall

which (in abbreviated form) would check recursively all files and directories starting from directories matching the wildcard (e.g. `/usr/local/bin', `/usr/ucb/bin'). By default, fixall causes the permissions and ownership of the files to be fixed without further warning.

One problem with symbolic links is that the files they point to can get deleted leaving a `hanging pointer'. Since cfagent can make many hundreds of links without any effort, there is the danger that, in time, the system could become full of links which don't point anywhere. To combat this problem, you can set the option links=tidy in the files section. If this is set, cfagent will remove any symbolic links which do not point to existing files (see Reference manual).

The creation of symbolic links is illustrated in figure 1 and the checking algorithm was discussed in section 2. In addition to the creation of single links, one may also specify the creation of multiple links with a single command. The command

 
links:

   binaryhost::

      /local/elm/bin +> /local/bin

links all of the files in `/local/elm/bin' to corresponding files in `/local/bin'. This provides, amongst other things, one simple way of installing software packages in regular `bin' directories without controlling users' PATH variable. A further facility makes use of cfagent's knowledge of available (mounted) binary resources to search for matches to specific links. Readers are referred to the full documentation concerning this feature.

The need to tidy junk files has become increasingly evident during the history of cfengine. Files build up quickly in areas like `/tmp', `/var/tmp'. Many users use these areas for receiving large ftp-files so that their disk usage will not be noticed! To give another example, just in the last few months the arrival of netscape World Wide Web client, with its caching facilities, has flooded hard-disks at Oslo with hundreds of megabytes of WWW files. In addition the regular appearance of `core' files(1) and compilation by-products (`.o' files and `.log' files etc.) fills disks with large files which many users do not understand. The problem is easily remedied by a few lines in the cfagent configuration. Files can be deleted if they have not been accessed for n-days. Recursive searches are both possible and highly practical here. In following example:

 
tidy:

   AllHomeServers::

      home                 pattern=core       r=inf age=0
      home/.wastebasket    pattern=*          r=inf age=14
      home/.netscape-cache pattern=cache????* r=inf age=2
      home/.MCOM-cache     pattern=cache????* r=inf age=2
      home/.netscape       pattern=cache????*  r=inf age=2

all hosts in the group `AllHomeServers' are instructed to iterate over all users' home directories (using the wildcard home) and look for files matching special patterns. Cfagent tests the access time of files and deletes only files older than the specified limits. Hence all core files, in this example, are deleted immediately, whereas files in the subdirectory `.wastebasket' are deleted only after they have lain there untouched for 14 days, and so on.

As a system administrator you should, of course, exercise great caution when making rules which can delete users' files. A single slip of the hand can result in a rule which will irretrievably delete files.

When making a `tidy' strategy you should probably coordinate with your backup policy. You should not delete files until after you have taken a backup, so that -- if the worst should happen -- you are covered against possible accidents.

Cfagent helps to some extent to keep track of what files it deletes. When tidying users' home directories it creates a log file of all files which were deleted on the last tidy operation. This log is called ~/.cfengine.rm.

You might consider tidying certain files only once a week, in which case a command such as

 
tidy:

   AllHomeServers.Sunday::

       files to tidy

could be useful. Nonsense files, such as `core' files could be tidied every night.

NOTE! Be careful when telling cfagent to delete core files. If you write a wildcard like core*, then you could risk deleting important system files such as core.h.


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