user: In Linux, "user" can have a few different but related meanings depending on the context. <That's probably an unnecessary statement.> Normally a user is a person who can use the Linux system, because a user account has been set up for them (and they know the name of the user account and password).

All files are owned by a user (account), and access permissions can be assigned to the owner. File permissions can also be assigned to a group, which consists of one or more user (accounts).

A user can be a real person, or an "artificial" person established for purposes of controlling permissions on executable programs or files. For example, a system typically has a user account established to be the "owner" of the Apache web server (sometimes "nobody" (not recommended because "nobody" is often used as the owner of other executable files -- if somebody breaks in and becomes established as user "nobody" he can run any programs that "nobody" has executable permissiion for, or change any files that "nobody" has write permission for), sometimes "www-<something", "apache", or ??).

<Maybe the previous paragraph should be moved to the file ownership and permissions in Linux discussion, along with:> Having the wrong owner, group, or permissions is a common cause of programs failing to work in Linux. Wrong permissions on an executable are probably the most obvious possibility, but consider that wrong permissions on, for example, a configuration file will mean that the program cannot access its configuration file.

Contributors

• RandyKramer - 31 Jan 2002
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