Home and other directories

Each departmental account has a home directory to store personal files. Most applications also store their configuration in your home directory once you start using them.

Besides your home directory, most research groups also have some other locations where data can be stored, some for private/personal data, others for shared use.

How to Access

• Files and directories are physically stored on a server, mostly one of your research group. Some directories (but certainly your home directory) are made available to other system group administered computers by means of NFS and automounter. This means that on those computers you can use/access these files and directories as if they were attached locally to the computer you are working on.
  In this way, on system group administered computers your home directory is always accessible via /home/yourloginname.
  Home directories are initially created with mode 0700 (only accessible to the owner). A daily script checks the mode and if necessary makes the directory not writable for members of the group and others. In this case a mail is sent to the owner.
• Some storage locations are also accessible from any departmental computer (both self and system group administered) by means of Samba.
• Because most system group administered systems can be reached by SSH (certainly from within departmental networks), you can also access the storage available on/to them by means of SSHFS.

Disk Quota

• Some storage locations (but certainly your home directory) are limited with disk quota.
  • Take care not to put too much data there because that might interfere with normal operation of your applications: once your quota is used, you will not be able to write additional (data to) files and you risk losing important stuff when approaching that limit even to the extent that (the configuration of) some applications becomes inconsistent and un-usable.
  • Ask around in your research group whether or not there are better storage locations to store (large volumes of) data.

Backup

• Some storage locations (but certainly your home directory) are backuped.
  • You can recover deleted files or previous versions of changed files (to a reasonable extent of course)

Automounter and physical location of directories

On most system group administered machines NFS and automounter are used. This means that remote directories can be accessed as if they were attached locally. Our automounter is configured to use the top-level directories /home and /cw.

What the real/physical location of the directory /home/X is, can be found with the command:

ypmatch X auto.home

This is mostly something of the form:

HOST:/export/home1/&

This means that /home/X really is the directory /export/home1/X that it is located on the machine HOST.

You should avoid to use the real path /export/home1/X because that will only work on the machine HOST itself. You should use /home/X as much as possible because that works on all machines that use NFS and have access to (/export on) HOST.

Besides /home/X, which is mostly used for personal home directories, there are also directories that are accessible via /cw/X.

Their interpretation and use is exactly the same as for /home/X as explained above.

You can find the real/physical location of /cw/X with:

ypmatch X auto.cw

/home and /cw seem empty

This is a consequence and normal behaviour of the automounter.

For Unix/Linux, to "mount a directory" means that the directory structure is attached to (a node in) the local file system such that everything from that directory structure is available beneath that node it is mounted on.

In this way, you can mount the remote directory /export/home1/X from the machine HOST using NFS on /home/X on your local machine.

Because it takes too many resources (CPU cycles, open file descriptors, network packets, ...) to keep all remotely available directories mounted on every machine, these directories are only mounted (automatically) when needed. Moreover they are un-mounted (also automatically) when they are not in use any more on the machine they were mounted on. This process of mounting and unmounting is managed by the automounter.

Consequently /home/X seems not to exist until some process needs it ... whenever a process tries to access it, this request will be picked up by the automounter, the remote file system in question will be mounted and the process will be given access as if the directory was there all the time. If the process releases whatever it needed on that directory, the automounter will notice it (after a time-out of course, not immediately to avoid excessive un-mount - mount activity) and will un-mount the remote directory which makes /home/X seem to disappear again.

Doing a simple ls /home or ls /cw is therefore not a good indication to see if a specific directory exists. If you know the name with which the directory is known to the automounter, you can test the availability of the directory with ls /home/X/ or ls /cw/X/. Do notice the trailing / which usually is needed to convince the automounter that you really want to access the specified directory ... without that trailing / some automounters will not actually mount the directory but only show its contents if it is already mounted.