What is Cygserver?
Cygserver is a program which is designed to run as a background service.
It provides Cygwin applications with services which require security
arbitration or which need to persist while no other cygwin application
is running.
The implemented services so far are:
- Control slave tty/pty handle dispersal from tty owner to other
processes without compromising the owner processes' security.
- XSI IPC Message Queues.
- XSI IPC Semaphores.
- XSI IPC Shared Memory.
- Allows non-privileged users to store obfuscated passwords in the
registry to be used for setuid(2) to create user tokens with network
credentials. This service is used by `passwd -R'. Using the stored
passwords in setuid(2) does not require running cygserver. The
registry storage is the same as Windows uses to store passwords for
accounts running Windows services.
Cygserver command line options:
Options to Cygserver take the normal UNIX-style `-X' or `--longoption' form.
Nearly all options have a counterpart in the configuration file (see below)
so setting them on the command line isn't really necessary. Command line
options override settings from the Cygserver configuration file.
The one-character options are prepended by a single dash, the long variants
are prepended with two dashes. Arguments to options are marked in angle
brackets below. These are not part of the actual syntax but are used only to
denote the arguments. Note that all arguments are required. Cygserver
has no options with optional arguments.
The options recognized are:
-f, --config-file <file>
Use <file> as configuration file instead of the default configuration
line. The default configuration file is /etc/cygserver.conf, typically.
The --help and --version options will print the default configuration
pathname.
This option has no counterpart in the configuration file, for obvious
reasons.
-c, --cleanup-threads <num>
Number of threads started to perform cleanup tasks. Default is 2.
Configuration file option: kern.srv.cleanup_threads
-r, --request-threads <num>
Number of threads started to serve application requests. Default is 10.
The -c and -r options can be used to play with Cygserver's performance
under heavy load conditions or on slow machines.
Configuration file option: kern.srv.request_threads
-p, --process-cache <num>
Number of processes which can connect concurrently to cygserver.
Default is 62. Each process connected to cygserver is a synchronization
object which has to be maintained. The data structure to maintain these
processes is the so-called "process cache". In theory, an arbitrary
number of processes could connect to cygserver, but due to the need to
synchronize, the higher the number of connected processes, the more
synchronization overhead exists. By using this option, you can set an
upper limit to the synchronization effort. If more than 62 processes
try to connect to cygserver concurrently, two additional synchronization
threads are necessary, and one for each further 62 concurrent
processes. So, useful values for the --process-cache option are 62, 124,
186, 248, 310. 310 is the maximum value.
Configuration file option: kern.srv.process_cache_size
NOTE: The number of child processes of a single parent process is limited
to 256. So in case of taking advantage of a process cache size beyond 256,
keep in mind that not all of these processes can be child processes of one
single parent process.
-d, --debug
Log debug messages to stderr. These will clutter your stderr output with
a lot of information, typically only useful to developers.
-e, --stderr
Force logging to stderr. This is the default if stderr is connected to
a tty. Otherwise, the default is logging to the system log. By using
the -e, -E, -y, -Y options (or the appropriate settings in the
configuration file), you can explicitely set the logging output as you
like, even to both, stderr and syslog.
Configuration file option: kern.log.stderr
-E, --no-stderr
Don't log to stderr. Configuration file option: kern.log.stderr
-y, --syslog
Force logging to the system log. This is the default, if stderr is not
connected to a tty, e. g. redirected to a file.
-Y, --no-syslog
Don't log to syslog. Configuration file option: kern.log.syslog
-l, --log-level <level>
Set the verbosity level of the logging output. Valid values are between
1 and 7. The default level is 6, which is relatively chatty. If you set
it to 1, you will get only messages which are printed under severe conditions,
which will result in stopping Cygserver itself.
Configuration file option: kern.log.level
-m, --no-sharedmem
Don't start XSI IPC Shared Memory support. If you don't need XSI IPC
Shared Memory support, you can switch it off here.
Configuration file option: kern.srv.sharedmem
-q, --no-msgqueues
Don't start XSI IPC Message Queues.
Configuration file option: kern.srv.msgqueues
-s, --no-semaphores
Don't start XSI IPC Semaphores.
Configuration file option: kern.srv.semaphores
-S, --shutdown
Shutdown a running daemon and exit. Other methods are sending a SIGHUP
to the Cygserver PID or, if running as service under NT, calling
`net stop cygserver' or `cygrunsrv -E cygserver'.
-h, --help
Output usage information and exit.
-v, --version
Output version information and exit.
How to start Cygserver:
Before you run Cygserver for the first time, you should run the
/usr/bin/cygserver-config script once. It creates the default
configuration file and, upon request, installs Cygserver as service
when running under NT. The script only performs a default install,
with no further options given to Cygserver when running as service.
Due to the wide configurability by changing the configuration file,
that's typically not necessary.
It's best practice to run Cygserver as a service under LocalSystem
account. This is the way it is installed for you by the
/usr/bin/cygserver-config script.
How to use the Cygserver services:
The Cygserver services are used by Cygwin applications only if you
set the environment variable CYGWIN to contain the string "server".
You must do this before starting the application.
Typically, you don't need any other option, so it's ok to set CYGWIN
just to "server". It is not necessary to set the CYGWIN environment
variable prior to starting the Cygserver process itself, but it won't
hurt to do so.
The easiest way is to set the environment variable CYGWIN to the values
you want in the Windows system environment and to reboot the machine.
This is advisable, since it allows you to set the variable once and
then forget about it. It also ensures that services as well as desktop
applications have the same setting.
If you don't want that for whatever reason, you can set the
variable in the /cygwin.bat file which is used in the net distribution,
to start a Cygwin bash from the desktop. In that file, you can set
the CYGWIN variable using Windows command line interpreter syntax, e. g.:
set CYGWIN=server
If you don't set CYGWIN in the system environment, but you're running
other Cygwin services, these services need to get that CYGWIN value by
setting the environment using the appropriate cygrunsrv option '-e' when
installing the service. Example installing a service 'foo':
cygrunsrv -I foo -p /usr/sbin/foo -e "CYGWIN=server"
The Cygserver configuration file:
Cygserver has many options, which allow to customize the server
to your needs. Customization is accomplished by editing the configuration
file, which is by default /etc/cygserver.conf. This file is read only
once on startup of Cygserver. There's no option to re-read the file on
runtime by, say, sending a signal to Cygserver.
The configuration file determines how Cygserver operates. There are
options which set the number of threads running in parallel, options
for setting how and what to log and options to set various maximum
values for the IPC services.
The default configuration file delivered with Cygserver is installed
to /etc/defaults/etc. The /usr/bin/cygserver-config script copies it to
/etc, giving you the option to overwrite an already existing file or to
leave it alone. Therefore, the /etc file is safe to be changed by you,
since it will not be overwritten by a later update installation.
The default configuration file contains many comments which describe
everything needed to understand the settings. A comment at the start of the
file describes the syntax rules for the file. The default options are shown
in the file but are commented out.
It is generally a good idea to uncomment only options which you intend to
change from the default values. Since reading the options file on Cygserver
startup doesn't take much time, it's also considered good practice to keep
all other comments in the file. This keeps you from searching for clues
in other sources.
If you have problems with Cygserver, or you have found a bug, or you
think you have found a bug, or you don't understand configuration file
options, the mailing list <cygwin@cygwin.com> is the right place to ask
questions.
Have fun!
