sendmail, 4th Edition

U=

Run agent as user-id:group-id V8.7 and later

Prior to V8.7, the user and group identities under which sendmail ran were defined by an elaborate set of properties (described under the F=S delivery agent flag in F=S on page 780). Beginning with V8.7, sendmail now offers the U= delivery agent equate as the means to define those identities. If the U= delivery agent equate is specified, it sets the default user and group identities for the delivery agent and always overrides the values of the DefaultUser option (DefaultUser on page 1000). If the F=S delivery agent flag is not set, any controlling user will override this U= delivery agent equate.

The form of the U= delivery agent equate looks like this:

U=user:group

Here, user is the alphanumeric identity of a user on the local system. The user is looked up with the method defined by the MailboxDatabase option (MailboxDatabase on page 1042).^[285] If user is found, the numeric user-id returned becomes the value used. Otherwise, user, which must be fully numeric, becomes the value used.

The colon,^[286] if present, is followed by the alphanumeric identity of a group on the local system. If group is found in the local group(5) file, the numeric group-id from that file is used. Otherwise, group, which must be fully numeric, becomes the value used. If the colon and group are missing and if user was found when looked up, the value is taken from the group-id returned by the lookup.

Some delivery agents provide mc macros with which to add a U= equate. ...