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NAME="DAEMONOV"
>The GDM Daemon</A
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><P
> 
	GDM was written with simplicity and security in mind. The
	overall design concept is this: 
      </P
><P
> 
	Upon startup the <TT
CLASS="FILENAME"
>gdm</TT
> daemon parses its config file
	<TT
CLASS="FILENAME"
>gdm.conf</TT
>.  For each of the local displays <TT
CLASS="FILENAME"
>gdm</TT
>
	forks an Xserver and a slave process. The main <TT
CLASS="FILENAME"
>gdm</TT
> process
	will then listen to XDMCP requests from remote displays and
	monitor the local display sessions.
      </P
><P
> 
	The <TT
CLASS="FILENAME"
>gdm</TT
> slave process opens the display and starts
	<TT
CLASS="FILENAME"
>gdmlogin</TT
>, the graphical login
	program. <TT
CLASS="FILENAME"
>gdmlogin</TT
> runs as a dedicated
	user and communicates asynchronously with the slave process
	through a pipe.
      </P
><P
> 
	GDM relies heavily on the presence of PAM, Pluggable
	Authentication Modules, but supports regular crypt() 
	and shadow passwords on legacy systems.
      </P
><P
>	Remote displays can connect to the XDMCP port on the GDM
	host. <TT
CLASS="FILENAME"
>gdm</TT
> will grant access to hosts specified in
	the gdm service section in your TCP Wrappers configuration
	file. GDM does not support remote display access control on
	systems without TCP Wrappers. XDMCP support can be turned off
	completely, however.
      </P
><P
>	GDM includes several measures making it more resistant to
	denial of service attacks on the XDMCP service. A lot of the
	protocol parameters, handshaking timeouts etc. can be fine
	tuned. The defaults should work for most systems, however.
	Don't change them unless you know what you're doing.
      </P
><P
>	In general GDM is very reluctant regarding reading/writing of
	user files. For instance it refuses to touch anything but
	regular files.  Links, sockets and devices are ignored.  The
	value of the RelaxPermissions parameter determines whether GDM
	should accept files writable by the user's group or others.
	These are ignored by default.
      </P
><P
>	All operations on user files are done with the effective
	userid of the user. If the sanity check fails on the user's
	<TT
CLASS="FILENAME"
>.Xauthority</TT
> file, a fallback cookie is created in
	<TT
CLASS="FILENAME"
>/tmp</TT
>.
      </P
><P
>	Finally, the sysadmin can specify the maximum file size GDM
	should accept, and, if the face browser is enabled, a tunable
	maximum icon size is also enforced.  On large systems it is
	still advised to turn off the face browser for performance
	reasons. Looking up icons in homedirs, scaling and rendering
	face icons can take quite a long time. YMMV.
      </P
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