Classic Shell Scripting

Other Real-World Issues

There are some other issues that are likely to come up in the Real World. For the sake of brevity we wimp out, and instead of writing code, we simply discuss them here.

First, and most obvious, is that the /etc/group file is also likely to need merging. With this file, it's necessary to:

• Make sure that all the groups from each individual system exist in the merged /etc/group file, and with the same unique GID. This is completely analogous to the username/UID issue we just solved, only the format of the file is different.

• Do a logical merge of users in the same group on the different systems. For example:

floppy:x:5:tolstoy,camus                 In u1 /etc/group
floppy:x:5:george,betsy                  In u2 /etc/group

• When the files are merged, the entry for group floppy needs to be:

floppy:x:5:tolstoy,camus,george,betsy     Order of users doesn't matter

• The GID of all files must be brought into sync with the new, merged /etc/group file, just as was done with the UID. If you're clever, it's possible to generate the find ... | xargs chown ... command to include the UID and GID so that they need to be run only once. This saves machine processing time at the expense of additional programming time.

Second, any large system that has been in use for some time will have files with UID or GID values that no longer (or never did) exist in /etc/passwd and /etc/group. It is possible to find such files with:

find / '(' -nouser -o -nogroup ')' -ls

This produces a list of files in an output format similar to that of ...