You can edit the field by editing the file, or you can use
usermod -c, although nowadays it is called the
comment field in
man 5 passwd, this was not always the case, it used to be the GECOS field on UNIX, although that
name did not reflect the use it had: providing general information.
The proper population is a comma separated list of four (possible empty) strings. You still see this in how some programs create this part of the passwd entry, pre-seeding it with
The first of those fields should contain the full user name (or program name if used for a daemon etc.); the second the physical location; the third (office) telephone; and the fourth home phone (sometimes telex/fax).
finger can be used to display a persons information, including the structured contents of that field. I have actually used that feature (with Yellow Pages to get information available on all workstation), before the advent of LDAP and personal address books.