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Files and transfer

Basics

Your home directory on SRCF servers is /home/<crsid> and is private to you. Group account files can be found at /societies/<groupname> and can only be accessed by group account admins.

All accounts also come with a ‘public’ directory (these are located at /public/home/<crsid> and /public/societies/<groupname> respectively). This includes your website root public_html, but you’re free to use them as you wish.

You can use SFTP or SCP to transfer files between your SRCF account and your personal computer. Mac and Linux come with scp for per-file transfer; you may prefer a graphical client – options include WinSCP on Windows, or Cyberduck for Mac/Windows.

Quotas

We provide users with 2GB of space for their personal files, and each group account also comes with 2GB of its own space. If you run out, you may request additional quota from the sysadmins. For larger increases, you may be asked to justify the need, and the SRCF committee may need to approve it.

Consider searching for cache files in your home directory that may be taking up unnecessary space, or compressing large files (e.g. high-resolution photos on websites).

You can use the srcf-quota command over SSH to check your current quota and usage. You’ll also receive email notifications when you approach your quota. Once the hard limit is reached, you’ll no longer be able to create or append to files.

Ownership and permissions

Each file or directory stored on the SRCF have two ownership fields associated with it: an owner (a system user) and a group (a system group; this is distinct from SRCF group accounts). Every user has an associated personal group (e.g. the user spqr2 also has a corresponding group spqr2), whilst admins of a group account will be members of an additional system group.

By default, your home directory /home/<crsid> is private to you, and group account home directories like /societies/<groupname> are private to their current admins. In contrast, the public directories /public/home/<crsid> and /public/societies/<groupname> are world-readable, meaning their contents are visible to any SRCF user. Because websites are served from here, you should ensure any files containing sensitive information (such as credentials for databases) are individually set to not be world-readable.

See also group permissions.

World-writable files

World writable files are files that anybody on the system can write to (edit). Whilst in general you can trust other SRCF users not to modify your files, there are several reasons why world-writable files are a problem:

  • People make mistakes. For instance, if you have a world-writable directory, and somebody runs rm -r / by mistake (this has happened at least once) then all the files in that directory will be deleted.
  • Users’ accounts may have been compromised. We have had one incident where a worm entered the computer via an insecure society website and proceeded to overwrite every world-writable file on the computer.
  • World writable files make things easier for attackers. If for instance a directory underneath your public_html directory is world-writable then an attacker able to write files on the system could place a script there containing commands that he could execute as you.

To avoid problems like this you should avoid creating world-writable files and directories, and if you have created them then you change them to be non-world-writable. You can do this using the chmod command – chmod o-w filename will remove world-writable permissions from a file and chmod -R o-w ~ will do the same for all world-writable files in your home directory.

Some CGI scripts will tell you that they need to have world-writable files / directories to work. This is almost certainly not the case on the SRCF system where CGI / PHP scripts run as the user that owns them rather than the webserver. For society accounts it is often necessary to make the files group-writable rather than world-writable (presuming that the intended effect is to allow multiple members of the society to write to them). If you can’t get a script to work without world-writable files / directories then get in touch with the support team and we’ll see what we can do to help.

Snapshots

Although the SRCF does not guarantee to take backups of users’ data, snapshots of /home, /public and /societies are generally taken regularly for disaster recovery purposes. Snapshots may be accessed using the hidden (it will not show up in ls -a or in shell autocomplete) directory .snapshot, available at any level of the file hierarchy. For example:

    spqr2@pip:~$ ls -lut .snapshot
    total 336
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 18:00 sv_hourly.0
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 17:00 sv_hourly.1
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 16:00 sv_hourly.2
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 15:00 sv_hourly.3
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 14:00 sv_hourly.4
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 13:00 sv_hourly.5
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 12:00 sv_hourly.6
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 11:00 sv_hourly.7
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 10:00 sv_hourly.8
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 09:00 sv_hourly.9
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 08:00 sv_hourly.10
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 07:00 sv_hourly.11
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 06:00 sv_hourly.12
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 05:00 sv_hourly.13
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 04:00 sv_hourly.14
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 03:00 sv_hourly.15
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 02:00 sv_hourly.16
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 01:00 sv_hourly.17
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 01:00 sv_daily.0
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  6 00:00 sv_hourly.18
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  5 23:00 sv_hourly.19
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  5 22:00 sv_hourly.20
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  5 21:00 sv_hourly.21
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  5 20:00 sv_hourly.22
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  5 19:00 sv_hourly.23
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  5 01:00 sv_daily.1
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  4 01:00 sv_weekly.0
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  4 01:00 sv_daily.2
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  3 01:00 sv_daily.3
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  2 01:00 sv_daily.4
    drwxr-x--- 2 spqr2 spqr2 8192 Jul  1 01:00 sv_daily.5
    drwxr-x--- 2 spqr2 spqr2 8192 Jun  2 01:00 sv_daily.6
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 29 01:00 sv_daily.7
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 28 01:00 sv_daily.8
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 27 01:00 sv_weekly.1
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 27 01:00 sv_daily.9
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 26 01:00 sv_daily.10
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 25 01:00 sv_daily.11
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 24 01:00 sv_daily.12
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 23 01:00 sv_daily.13
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 20 01:00 sv_weekly.2
    drwxr-x--- 2 spqr2 spqr2 8192 Jun 13 01:00 sv_weekly.3

Note that snapshots are named sv_[type].[index], with index 0 indicating the most recent snapshot of that type. The listing above shows 24 hourly, 14 daily and 4 weekly snapshots; you may see fewer or more than this.

Snapshots preserve file permissions and are read-only, so if you wish to retrieve something from a snapshot, you must have had permission to access it at the time the snapshot was taken, and must copy (rather than move) it out of the snapshot.

Snapshots going further back in time may be available on an off-site disaster-recovery replica; if you need access to these, contact the sysadmins (but please don’t count on them being available; you should take your own backups regardless).


Last modified on Thursday May 6, 2021 by Matias Silva