userv options [--] service-user service-name [argument ...] userv options -B|--builtin [--] builtin-service [info-argument ...]
service-user specifies which user is to provide the service. The user may be a login name or a numeric uid, or - to indicate that the service user is to be the same as the calling user.
The service name is interpreted by the userv daemon on behalf of the service user. It will often be the name of a program.
Single-letter options may be combined as is usual with Unix programs, and the value for such an option may appear in the same argument or in the next.
--overrideoption to specify a string consisting of
execute-builtinfollowed by the builtin-service requested, and requesting a service user of - (indicating the calling user). If the builtin service being requested requires a service-argument then this must be supplied to the client in the same argument as the builtin-service. See Directives for changing execution settings, subsection 4.2.4 for details of the builtin services available, and Security-overriding options, section 2.2 for details of the
--overrideoptions. The actual service name passed will be the builtin-service; note that this actual service name (as opposed to the override data) and the info-arguments supplied will be ignored by most builtin services; the override mechanism and
execute-builtinwill be used to ensure that the right builtin service is called with the right service-arguments.
catinvoked by the client; the other file descriptor passed to
catwill be one inherited by the client program from the caller or one opened by the client program on behalf of the caller. The descriptor in the service program that should be connected must be specified as fd, either as a decimal number or as one of the strings stdin, stdout or stderr. The next argument is a filename which will be opened by the client with the privileges of the calling user. modifiers is used to specify whether the file or descriptor is to be read from or written to. It consists of a series of words separated by commas. A comma may separate the modifiers from the fd and is required if fd is not numeric.
The modifier words are:
If no modifiers which imply read or write are used it is as if write had been specified, except that if the filedescriptor 0 of the service is being opened (either specified numerically or with stdin) it is as if overwrite had been specified (or write if only fd was specified).
The client will also use O_NOCTTY when opening files specified by the caller, to avoid changing its controlling terminal.
By default stdin, stdout and stderr of the service will be connected to the corresponding descriptors on the client. Diagnostics from the client and daemon will also appear on stderr.
If wait is specified, the client will wait for the pipe to be closed, and only exit after this has happened. This means that either the receiving end of the pipe connection was closed while data was still available at the sending end, or that the end of file was reached on the reading file descriptor. Errors encountered reading or writing in the client at this stage will be considered a system error and cause the client to exit with status 255, but will not cause disconnection at the service side since the service has already exited.
If close is specified the client will immediately close the pipe
connection by killing the relevant copy of
cat. If the service
uses the descriptor it will get
EPIPE) for a
writing descriptor or end of file for a reading one; the descriptor
opened by or passed to the client will also be closed.
If nowait is specified then the client will not wait and the connection will remain open after the client terminates. Data may continue to be passed between the inheritors of the relevant descriptor on the service side and the corresponding file or descriptor on the client side until either side closes their descriptor. This should not usually be specified for stderr (or stdout if --signals stdout is used) since diagnostics from the service side may arrive after the client has exited and be confused with expected output.
The default is wait for writing file descriptors and close for reading ones.
--fdwaitoption - even by a
--filewhich does not specify an action on termination (in this case the default will be used, as described above).
_exit, so that only numbers from 0 to 255 can be returned and not the full range of numbers and signal indications which can be returned by the
waitfamily of system calls.)
The method may be one of the following:
Problems such as client usage errors, the service not being found or permission being denied or failure of a system call are system errors. An error message describing the problem will be printed on the client's stderr, and the client's exit status will be 255. If the client dies due to a signal this should be treated as a serious system error.
SIGPIPEthe exit status of the client will be zero, even if it would have been something else according to the exit status method specified. This option has no effect on the code and description printed if the exit status method stdout is in use.
There are also some options which are available for debugging and to allow the system administrator to override a user's policy. These options are available only if the client is called by root or if the calling user is the same as the service user.