NAME
userv - request user services
SYNOPSIS
userv [option ...] [--] service-user service-name [argument ...]
userv [option ...] -B | --builtin [--] builtin-service
[info-argument ...]
DESCRIPTION
userv is used to have a task performed under different userid while
maintaining limited trust between caller and callee.
service-user specifies which user account is to perform the task. 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. This is controlled by configuration files in the service
user’s filespace; consult the userv specification for details.
OPTIONS
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.
-B | --builtin
Requests that a builtin service be provided. This is
equivalent to using the --override option to specify a string
consisting of ‘execute-builtin’ followed 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 the
specification, or the output of
userv -B help
for details of the builtin services available, and below for
details of the --override options.
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-builtin’ will be used to ensure that the right
builtin service is called with the right service-arguments.
-f | --file fd[fdmodifiers]=filename
Requests that data be copied in and out of the service using
pipes. For each file or descriptor this will be done by
creating a pipe, one end of which is passed to the service
program and the other end of which is passed to a copy of cat
invoked by the client; the other file descriptor passed to
cat will 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:
read O_RDONLY: Allow reading and not writing.
May not be used with ‘write’ or things that
imply it.
write O_WRONLY: Allow writing and not reading.
Doesnt truncate or create without
‘truncate’ or ‘create’. ‘write’ or things
that imply it may not be used with ‘read’.
overwrite Equivalent to ‘write,create,truncate’.
create, creat O_CREAT: Creates the file if necessary.
Implies ‘write’.
exclusive, excl O_EXCL: Fails if the file already exists.
Implies write and create. May not be used
with ‘truncate’.
truncate, trunc O_TRUNC: Truncate any existing file.
Implies ‘write’. May not be used with
‘exclusive’.
append O_APPEND: All writes will append to the
file. Implies ‘write’ (but not ‘create’).
sync O_SYNC: Do writes synchronously. Implies
‘write’.
wait, nowait, close
These modifiers control the behaviour of
the client, with respect to the pipes
carrying data to and from the service, when
the service terminates. See below.
fd The filename is not a filename but a
numeric file descriptor. One or both of
‘read’ and ‘write’ must be specified, and
no other words are allowed. The filename
may also be ‘stdin’, ‘stdout’ or ‘stderr’
for file descriptor 0, 1 or 2 respectively.
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 SIGPIPE (or 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.
-w | --fdwait fd=action
Sets the action on termination of the service for the
specified file descriptor; action must be ‘wait’, ‘nowait’ or
‘close’ as described above. The file descriptor must be
specified as open when this option is encountered; this
option is overridden by any later --file or --fdwait option -
even by a --file which does not specify an action on
termination (in this case the default will be used, as
described above).
-D | --defvar name=value
Set a user-defined variable name to value. These user-
defined variables are made available in the configuration
language as the parameters ‘u-name’ and are passed to the
service in environment variables USERV_U_name. name may
contain only alphanumerics and underscores, and must start
with a letter. If several definitions are given for the same
name then only the last is effective.
-t | --timeout seconds
Time out the service if it takes longer than seconds seconds
(a positive integer, in decimal). Timeout will produce a
diagnostic on stderr and an exit status of 255. If seconds
is zero then no timeout will be implemented (this is the
default).
-S | --signals method
Affects the handling of the exit status when the service
terminates due to a signal. (The client will always finish
by calling _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 wait() family of
system calls.)
The method may be one of the following:
status The client’s exit status will be status.
This will not be distinguishable from the
service really having exited with code
status. This method is the default, with a
status of 254.
number, number-nocore
The client’s exit status will be the number
of the signal which caused the termination
of the service. If ‘number’ is used rather
than ‘number-nocore’ then 128 will be added
if the service dumped core. ‘number’ is
very like the exit code mangling done by
the Bourne shell.
highbit The client’s exit status will be the number
of the signal with 128 added. If the
service exits normally with an exit code of
greater than 127 then 127 will be returned.
stdout The service’s numeric wait status as two
decimal numbers (high byte first) and a
textual description of its meaning will be
printed to the client’s standard output.
It will be preceded by a newline and
followed by an extra newline, and the
numbers are separated from each other and
from the textual description by single
spaces. The exit status of the client will
be zero, unless a system error occurs in
which case no exit status and description
will be printed to stdout, and an error
message will be printed to stderr as usual.
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.
-H | --hidecwd
Prevents the calling process’s current directory name from
being passed to the service; the null string will be passed
instead.
-P | --sigpipe
If the service program is terminated due to a SIGPIPE the
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.
-h | --help
Prints the client’s usage message.
--copyright
Prints the copyright and lack of warranty notice.
SECURITY-OVERRIDING OPTIONS
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.
--override configuration-data
--override-file file
Do not read the usual configuration files. Instead, the
client sends configuration-data (followed by a newline) or
the contents of filename (which is opened in the context of
the client) to the daemon and the daemon uses that data
instead. The configuration-data must all be in one argument.
It will have a single newline appended so that a single
directive can easily be given, but if more than one directive
is required it will have to contain one or more real
newlines.
--spoof-user user
Pretend to the service that it is being called by user (which
may be a username or a uid). This will also affect the group
and supplementary groups supplied to the service; they will
be the standard group and supplementary groups for user. The
--spoof-user option will not affect which user is chosen if
the service user is specified as just ‘-’; in this case the
service user will be the real calling user.
ENVIRONMENT
LOGNAME, USER These are used to determine the name of the calling
user, to be passed to the service in USERV_USER. Their
values will only be used if they correspond to the
calling UID.
FILES
/var/run/userv/socket UNIX-domain socket used for
communication between userv and uservd.
/var/run/userv/%x.%x.%x Pipes used for connecting file
descriptors in the client and the
service.
SEE ALSO
uservd(8)
Ian Jackson, User service daemon and client specification.
COPYRIGHT
GNU userv is Copyright (C)1996-2003,2006 Ian Jackson, except that this
manpage is Copyright (C)2000 Ben Harris and Copyright (C)2003 Ian
Jackson.
GNU userv is licensed under the terms of the GNU General Public Licence,
version 2 or (at your option) any later version, and it comes with NO
WARRANTY, not even the implied warranty of MERCHANTABILITY or FITNESS FOR
A PARTICULAR PURPOSE. See the GNU General Public License for details.
You should have received a copy of the GNU General Public License along
with userv, if not, write to the Free Software Foundation, 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA.
HISTORY
userv was initially written in 1996 by Ian Jackson. It became GNU userv
in 1999, and version 1.0 was released in 2000.