The daemon which is handling the service user side of things will read -configuration files to decide what to do. If it decides to allow the -service to be provided it will fork a subprocess to execute the -service. -
+configuration files to decide what to do. If it decides to allow the service +to be provided it will fork a subprocess to execute the service.-The service will have no controlling terminal, but it will be a -process group leader. -
+The service will have no controlling terminal, but it will be a process group +leader.
-If the client is killed or times out or a file or descriptor being
-read or written by the client process gets an error then the service
-will be disconnected from the client. The client will return an exit
-status of 255 and some the service's pipes may be closed at the other
-end. The service will become a child of init. The service may
-well not notice the disconnection, though writing to a pipe after this
-may produce a SIGPIPE and the facility exists to have a
-SIGHUP sent to the service on disconnection.
-
init. The service may well not notice the
+disconnection, though writing to a pipe after this may produce a
+SIGPIPE and the facility exists to have a SIGHUP sent
+to the service on disconnection.
-The service program's standard filedescriptors, and possibly other
-file descriptors, will be connected to pipes or to
-/dev/null. The userv client/daemon pair will arrange
-that data is copied between the files or file descriptors specified to
-to the client by the caller and these these pipes.
-
/dev/null. The
+userv client/daemon pair will arrange that data is copied between
+the files or file descriptors specified to to the client by the caller and
+these these pipes.
-Pipes which may be written to will be closed if a write error occurs
-on the corresponding client-side file or descriptor, which may result
-in a SIGPIPE in the service program; pipes open for reading
-will get EOF if the client-side file descriptor gets EOF
-or an error.
-
SIGPIPE in the service program; pipes open for reading will get
+EOF if the client-side file descriptor gets EOF or an
+error.
-If the service closes one of its reading file descriptors the writing
-end of the corresponding pipe will generate a SIGPIPE when
-attempts are made by the client/daemon pair to write to it. This will
-not be considered an error; rather, the relevant pipe will be
-discarded and the corresponding file or file descriptor held by the
-client will be closed.
-
SIGPIPE when attempts are
+made by the client/daemon pair to write to it. This will not be considered an
+error; rather, the relevant pipe will be discarded and the corresponding file
+or file descriptor held by the client will be closed.
-Likewise, if one of the file descriptors held by the client for
-writing by the service is a pipe whose other end is closed by the
-caller then the client/daemon pair will see an error when trying to
-copy data provided by the service. This too will not be considered an
-error; rather, the pipe correspondong to that descriptor will be
-closed and any further writes will cause the service to get a
-SIGPIPE.
-
SIGPIPE.
-Note that not all write errors or broken pipes on file descriptors may
-be visible to the service, since buffered data may be discarded by the
-operating system and there will be a finite interval between the error
-happening and the service being disconnected from the client or the
-next write causing a SIGPIPE.
-
SIGPIPE.
-Read errors on file descriptors (and disconnection) will only be
-visible to the service and distinguishable from normal end of file if
+Read errors on file descriptors (and disconnection) will only be visible to the
+service and distinguishable from normal end of file if
disconnect-hup is in effect.
-
-Read and write errors (other than broken pipes, as described above) -will always be visible to the caller; they are system errors, and will -therefore cause the client to print an error message to stderr and -return with an exit status of 255. -
+Read and write errors (other than broken pipes, as described above) will always +be visible to the caller; they are system errors, and will therefore cause the +client to print an error message to stderr and return with an exit status of +255.
-If the main service program process exits while it still has running
-children any file descriptors held by those children can remain open,
-depending on the use of wait, nowait or close for the
-relevant file descriptor in the client's arguments. By default
-writing filedescriptors remain open and the client will wait for them
-to be closed at the service end, and reading file descriptors are
-closed immediately. These leftover child processes will not get a any
-SIGHUP even if a read or write error occurs or the client
-disconnects before then.
-
SIGHUP even if a read
+or write error occurs or the client disconnects before then.
The service will have some information in environment variables: -
LOGNAME variable is
+LOGNAME variable is
set (or, if that is unset, if the USER variable is set) in the
-environment passed to the client by the caller then the password entry
-for that login name will be looked up; if that password entry's uid is
-the same as that of the calling process then that login name will be
-used, otherwise (or if neither LOGNAME nor USER is set)
-the calling process's uid will be looked up to determine their login
-name (and if this lookup fails then the service will not be invoked).
-
-USERV_GID. If no name can be found for any of the
-calling process's group(s) then the service will not be invoked.
-
-LOGNAME nor USER is set) the calling
+process's uid will be looked up to determine their login name (and if this
+lookup fails then the service will not be invoked).
+USERV_GID. If no name can be found for any of the calling
+process's group(s) then the service will not be invoked.
+--hidecwd flag was used then this variable will be set to an
-empty string (this is not considered an error).
-
---hidecwd flag was used then this variable will be set to an empty
+string (this is not considered an error).
+HOME, PATH, SHELL, LOGNAME and USER
-will be set appropriately (according to the details of the service
-user).
-
+
+HOME, PATH, SHELL, LOGNAME
+and USER will be set appropriately (according to the details of
+the service user).
+User service daemon and client specification
-0.62ian@davenant.greenend.org.uk
+