apache2中的httpd.conf的問題 - BBS

#
# If you wish httpd to run as a different user or group, you must run
# httpd as root initially and it will switch.
#
# User/Group: The name (or #number) of the user/group to run httpd as.
# . On SCO (ODT 3) use "User nouser" and "Group nogroup".
# . On HPUX you may not be able to use shared memory as nobody, and the
# suggested workaround is to create a user www and use that user.
# NOTE that some kernels refuse to setgid(Group) or semctl(IPC_SET)
# when the value of (unsigned)Group is above 60000;
# don't use Group #-1 on these systems!
#


這段文字不是很了解他的意思
有的書上建議User和Group設定www
可是有的書又建議設定為nobody
請問兩者有何不同呢?
這兩行設定是用來做什麼的
謝謝

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