scdaemon - Man Page

Smartcard daemon for the GnuPG system


scdaemon [--homedir dir] [--options file] [options] --server
scdaemon [--homedir dir] [--options file] [options] --daemon [command_line]


The scdaemon is a daemon to manage smartcards.  It is usually invoked by gpg-agent and in general not used directly.


Commands are not distinguished from options except for the fact that only one command is allowed.


Print the program version and licensing information.  Note that you cannot abbreviate this command.

--help,  -h

Print a usage message summarizing the most useful command-line options. Note that you cannot abbreviate this command.


Print a list of all available options and commands.  Note that you cannot abbreviate this command.


Run in server mode and wait for commands on the stdin.  The default mode is to create a socket and listen for commands there.


Run in server mode and wait for commands on the stdin as well as on an additional Unix Domain socket.  The server command GETINFO may be used to get the name of that extra socket.


Run the program in the background.  This option is required to prevent it from being accidentally running in the background.


--options file

Reads configuration from file instead of from the default per-user configuration file.  The default configuration file is named ‘scdaemon.conf’ and expected in the ‘.gnupg’ directory directly below the home directory of the user.

--homedir dir

Set the name of the home directory to dir. If this option is not used, the home directory defaults to ‘~/.gnupg’.  It is only recognized when given on the command line.  It also overrides any home directory stated through the environment variable ‘GNUPGHOME’ or (on Windows systems) by means of the Registry entry HKCU\Software\GNU\GnuPG:HomeDir.

On Windows systems it is possible to install GnuPG as a portable application.  In this case only this command line option is considered, all other ways to set a home directory are ignored.

To install GnuPG as a portable application under Windows, create an empty file named ‘gpgconf.ctl’ in the same directory as the tool ‘gpgconf.exe’.  The root of the installation is then that directory; or, if ‘gpgconf.exe’ has been installed directly below a directory named ‘bin’, its parent directory.  You also need to make sure that the following directories exist and are writable: ‘ROOT/home’ for the GnuPG home and ‘ROOT/var/cache/gnupg’ for internal cache files.


Outputs additional information while running. You can increase the verbosity by giving several verbose commands to gpgsm, such as ‘-vv’.

--debug-level level

Select the debug level for investigating problems.  level may be a numeric value or a keyword:


No debugging at all.  A value of less than 1 may be used instead of the keyword.


Some basic debug messages.  A value between 1 and 2 may be used instead of the keyword.


More verbose debug messages.  A value between 3 and 5 may be used instead of the keyword.


Even more detailed messages.  A value between 6 and 8 may be used instead of the keyword.


All of the debug messages you can get. A value greater than 8 may be used instead of the keyword.  The creation of hash tracing files is only enabled if the keyword is used.

How these messages are mapped to the actual debugging flags is not specified and may change with newer releases of this program. They are however carefully selected to best aid in debugging.

All debugging options are subject to change and thus should not be used by any application program.  As the name says, they are only used as helpers to debug problems.

--debug flags

Set debug flags.  All flags are or-ed and flags may be given in C syntax (e.g. 0x0042) or as a comma separated list of flag names. To get a list of all supported flags the single word "help" can be used. This option is only useful for debugging and the behavior may change at any time without notice.


Same as --debug=0xffffffff

--debug-wait n

When running in server mode, wait n seconds before entering the actual processing loop and print the pid.  This gives time to attach a debugger.


Enable debug output from the included CCID driver for smartcards. Using this option twice will also enable some tracing of the T=1 protocol.  Note that this option may reveal sensitive data.


This option disables all ticker functions like checking for card insertions.


For security reasons we won't create a core dump when the process aborts.  For debugging purposes it is sometimes better to allow core dump.  This option enables it and also changes the working directory to ‘/tmp’ when running in --server mode.


This option appends a thread ID to the PID in the log output.

--debug-assuan-log-cats cats

Changes the active Libassuan logging categories to cats.  The value for cats is an unsigned integer given in usual C-Syntax. A value of 0 switches to a default category.  If this option is not used the categories are taken from the environment variable ASSUAN_DEBUG.  Note that this option has only an effect if the Assuan debug flag has also been with the option --debug.  For a list of categories see the Libassuan manual.


Don't detach the process from the console.  This is mainly useful for debugging.

--listen-backlog n

Set the size of the queue for pending connections.  The default is 64. This option has an effect only if --multi-server is also used.

--log-file file

Append all logging output to file.  This is very helpful in seeing what the agent actually does.  Use ‘socket://’ to log to socket.


Use shared mode to access the card via PC/SC.  This is a somewhat dangerous option because Scdaemon assumes exclusive access to the card and for example caches certain information from the card.  Use this option only if you know what you are doing.

--pcsc-driver library

Use library to access the smartcard reader.  The current default on Unix is ‘’ and on Windows ‘winscard.dll’. Instead of using this option you might also want to install a symbolic link to the default file name (e.g. from ‘’). A Unicode file name may not be used on Windows.

--ctapi-driver library

Use library to access the smartcard reader.  The current default is ‘’.  Note that the use of this interface is deprecated; it may be removed in future releases.


Disable the integrated support for CCID compliant readers.  This allows falling back to one of the other drivers even if the internal CCID driver can handle the reader.  Note, that CCID support is only available if libusb was available at build time.

--reader-port number_or_string

This option may be used to specify the port of the card terminal.  A value of 0 refers to the first serial device; add 32768 to access USB devices.  The default is 32768 (first USB device).  PC/SC or CCID readers might need a string here; run the program in verbose mode to get a list of available readers.  The default is then the first reader found.

To get a list of available CCID readers you may use this command:

  echo scd getinfo reader_list \
    | gpg-connect-agent --decode | awk '/^D/ {print $2}'
--card-timeout n

This option is deprecated.  In GnuPG 2.0, it used to be used for DISCONNECT command to control timing issue.  Since DISCONNECT command works synchronously, it has no effect.


Please specify this option when the card reader supports variable length input for pinpad (default is no).  For known readers (listed in ccid-driver.c and apdu.c), this option is not needed.  Note that if your card reader doesn't supports variable length input but you want to use it, you need to specify your pinpad request on your card.


Even if a card reader features a pinpad, do not try to use it.


This option disables the use of admin class commands for card applications where this is supported.  Currently we support it for the OpenPGP card. This option is useful to inhibit accidental access to admin class command which could ultimately lock the card through wrong PIN numbers.  Note that GnuPG versions older than 2.0.11 featured an --allow-admin option which was required to use such admin commands.  This option has no more effect today because the default is now to allow admin commands.

--disable-application name

This option disables the use of the card application named name.  This is mainly useful for debugging or if a application with lower priority should be used by default.

--application-priority namelist

This option allows to change the order in which applications of a card a tried if no specific application was requested.  namelist is a space or comma delimited list of application names.  Unknown names are simply skipped.  Applications not mentioned in the list are put in the former order at the end of the new priority list.

To get the list of current active applications, use

    gpg-connect-agent 'scd getinfo app_list' /bye

All the long options may also be given in the configuration file after stripping off the two leading dashes.

Card Applications

scdaemon supports the card applications as described below.

The OpenPGP card application “openpgp”


This application is currently only used by gpg but may in future also be useful with gpgsm.  Version 1 and version 2 of the card is supported.

The specifications for these cards are available at
( and

The Telesec NetKey card “nks”


This is the main application of the Telesec cards as available in Germany.  It is a superset of the German DINSIG card.  The card is used by gpgsm.

The DINSIG card application “dinsig”


This is an application as described in the German draft standard DIN V 66291-1.  It is intended to be used by cards supporting the German signature law and its bylaws (SigG and SigV).

The PKCS#15 card application “p15”


This is common framework for smart card applications.  It is used by gpgsm.

The Geldkarte card application “geldkarte”


This is a simple application to display information of a German Geldkarte.  The Geldkarte is a small amount debit card application which comes with almost all German banking cards.

The SmartCard-HSM card application “sc-hsm”


This application adds read-only support for keys and certificates stored on a (, SmartCard-HSM).

To generate keys and store certificates you may use (, OpenSC) or the tools from (, OpenSCDP).

The SmartCard-HSM cards requires a card reader that supports Extended Length APDUs.

The Undefined card application “undefined”


This is a stub application to allow the use of the APDU command even if no supported application is found on the card.  This application is not used automatically but must be explicitly requested using the SERIALNO command.


$ scdaemon --server -v


There are a few configuration files to control certain aspects of scdaemons's operation. Unless noted, they are expected in the current home directory (see: [option --homedir]).


This is the standard configuration file read by scdaemon on startup.  It may contain any valid long option; the leading two dashes may not be entered and the option may not be abbreviated.  This default name may be changed on the command line (see: [option --options]).


If this file is present and executable, it will be called on every card reader's status change.  An example of this script is provided with the source code distribution.  This option is deprecated in favor of the DEVINFO --watch.


This file is created by scdaemon to let other applications now about reader status changes.  Its use is now deprecated in favor of ‘scd-event’.

See Also

gpg-agent(1), gpgsm(1), gpg(1)

The full documentation for this tool is maintained as a Texinfo manual. If GnuPG and the info program are properly installed at your site, the command

info gnupg

should give you access to the complete manual including a menu structure and an index.

Referenced By

gnupg(7), gpg-agent(1), gpg-card(1), gpgconf(1), gpg-connect-agent(1), gpg-preset-passphrase(1), watchgnupg(1).

2023-06-21 GnuPG 2.4.3 GNU Privacy Guard 2.4