Local transports handle deliveries to files and pipes. (The `autoreply' transport can be thought of as similar to a pipe.) Whenever a local transport is run, Exim forks a subprocess for it. Before running the transport code, it sets a specific uid and gid by calling `setuid()' and `setgid()'. It also sets a current file directory; for some transports a home directory setting is also relevant.
The values used for the uid, gid, and the directories may come from several different places. In many cases the director that handles the address associates settings with that address. However, values may also be given in the transport's own configuration, and these override anything that comes with the address. The sections below contain a summary of the possible sources of the values, and how they interact with each other.
All local transports have the options `group' and `user'. If `group' is set, it overrides any group that may be set in the address, even if `user' is not set. This makes it possible, for example, to run local mail delivery under the uid of the recipient, but in a special group. For example:
group_delivery:
driver = appendfile
file = /var/spool/mail/${local_part}
group = mail
If `user' is set, its value overrides what is set in the address. If `user' is non-numeric and `group' is not set, the gid associated with the user is used. If `user' is numeric, then `group' must be set.
The `pipe' transport contains the special option `pipe_as_creator'. If this is set and `user' is not set, the uid of the process that called Exim to receive the message is used, and if `group' is not set, the corresponding original gid is also used.
When the uid is taken from the transport's configuration, the `initgroups()' function is called for the groups associated with that uid if the `initgroups' option is set for the transport; `pipe' is the only transport that has such an option. When the uid is the one associated with the address by a director, the option for calling `initgroups()' is taken from the director: `aliasfile', `forwardfile', and `localuser' have this option.
When a router (as opposed to a director) sends a message to a local transport (for example, for batching) the uid and gid must be set on the transport. For directed addresses, if no uid is set in the transport, then one must be associated with the address by the director that handled it.
The `aliasfile' director has `group' and `user' options that can be used to specify the uid and gid for local deliveries directly generated by it.
The `forwardfile' director's `check_local_user' option causes a password file lookup for the local part of an address. The uid and gid obtained from this lookup are used for any local deliveries, but they can be overridden by the `group' and `user' options of the director.
The `localuser' director looks up local parts in the password file, and sets the uid and gid from that file for local deliveries.
The `smartuser' director has no means of associating a uid and gid with an address; consequently any local transport that it uses must specify them for itself.
The `pipe' transport has a `home_directory' option. If this is set, it overrides any home directory set by the director for the address. The value of the home directory is set in the environment variable HOME while running the pipe. It need not be set, in which case HOME is not defined.
The `appendfile' transport does not have a `home_directory' option. The only use for a home directory in this transport is if the expansion variable `$home' is used in one of its options, in which case the value set by the director is used.
The `appendfile' and `pipe' transports have a `current_directory' option. If this is set, it overrides any current directory set by the director for the address. If neither the director nor the transport sets a current directory, then Exim uses the value of the home directory, if set. Otherwise it sets the current directory to `/' before running a local transport.
The `aliasfile', `forwardfile', and `localuser' directors all have `current_directory' and `home_directory' options, which are associated with any addresses they explicitly direct to a local transport.
For `forwardfile', if `home_directory' is not set and there is a `file_directory' value, that is used instead. If it too is not set, but `check_local_user' is set, the user's home directory is used. For `localuser', if `home_directory' is not set, the home directory is taken from the password file entry that this director looks up. There are no defaults for `current_directory' in the directors, because it defaults to the value of `home_directory' if it is not set at transport time.
The `smartuser' director has no means of setting up home and current directory strings; consequently any local transport that it uses must specify them for itself if they are required.
Go to the first, previous, next, last section, table of contents.