Group write protocol
Last revision October 10, 2005
The system administrator can set up general directories within pangea for
group write access, allowing users to collaborate on projects without all the
usual swapping of files.
Although the directory has group write/delete permissions, individual
files in the directory may have more restrictive permissions. In
particular, individual files are normally created with permissions that
only allow the owner of the file -- not anyone else in the group -- to
update it. Others in the group can delete it or copy another file on
top of it, but they cannot simply update the existing file. This is a
consequence of
Unix file permissions.
Having write access to the directory allows you to create new files or
to delete entire files; but it does not allow you to modify an existing
file unless you also have write access on that specific file.
Another problem with group write access to a directory is the possibility
that two different accounts will attempt to update or replace the same file at
the same time. This leads to changes that "disappear" or to corrupted files.
To handle both problems listed above -- lack of write permission to modify
individual files, and potential for incompatible updates by multiple accounts
-- use this protocol for editing files in a group directory:
-
When you want to edit an existing file, first make a copy of the file in the
same directory, using the
.new
suffix. If you are logging in directly to pangea, you can use a command like:
cp -i file file.new
The
-i
option will notice if there is already a
file.new
and prompt you to overwrite it. If there is already a
file.new,
this means that someone else is already working on this file.
Do
not
overwrite his copy. Find out who he is
(ls -l
will show you the owning account) and coordinate your changes.
If there is no existing
file.new,
then the copy proceeds without incident. The fact that you have created the
file.new
copy now signals others in the group that you are working on this file
(assuming they all follow this same protocol).
If you are editing files with a Macintosh or PC program, you will have to
download a copy to your Macintosh or PC. In order to use this protocol,
immediately rename your local copy with the
.new
suffix and reload that copy
up to pangea. Now others can see that you are working on a copy.
-
Make your changes to the file and test it.
-
When ready to install your changed version, first rename the old one with a
.old
suffix, and then rename your new one to the original name.
For example, from a pangea login session, you could type commands like these:
mv file file.old
mv file.new file
Because you have write permission to the directory, you will be able to run
these
mv
commands whether or not you have specific write permission on that
individual file. Keeping the old version around for a while is good
insurance against editing mistakes.
If you are editing on your Macintosh or PC, first upload the latest version
of your
.new
copy, then rename the old version with the
.old
suffix and rename your
.new
copy to the normal name.
If you are mounting the
/WWW
directory as a file share on your
Windows PC
or
MacOS X
desktop, you can edit the file names directly.
If you are using an
scp or sftp
file transfer program, use the rename function in that program.
