Nobody (username)

In many Unix variants, "nobody" is the conventional name of a user account which owns no files, is in no privileged groups, and has no abilities except those which every other user has. Nobody typically either has a very high User ID, such as 32767, or uses a system User ID, typically between 1 and 100.

It is common to run daemons as "nobody", especially servers, in order to limit the damage that could be done by a malicious user who gained control of them. However, the usefulness of this technique is reduced if more than one daemon is run like this, because then gaining control of one daemon would provide control of them all. The reason is that "nobody"-owned processes have the ability to send signals to each other and even (on Linux) ptrace each other, which means that one process can read and write to the memory of another process. Creating one account for each daemon, as recommended by the Linux Standard Base, [Linux Standard Base, [http://refspecs.freestandards.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/usernames.html Core Specification 3.1 section 21.2: User & Group Names] ] provides for a tighter security policy.

ee also

*Privilege revocation
*Principle of least privilege

References