Manual Reference Pages - VGA_INIT (3)
vga_init - initialize svgalib library
It detects the chipset and gives up supervisor
rights. This is the recommended first line of any program that uses
can be called before it to avoid detection.
Svgalib catches a bunch of signals that usually kill your
program to restore textmode. If you catch signals before
vga_init() svgalib will restore textmode and prepare
for shutdown and then call your handler routine. If you dont
want this, catch the signal
after calling vga_init and do not daisychain to svgalibs original handler.
WARNING! svgalib needs two signals for its own purposes
(that is managing console switches). To avoid problems it uses
the otherwise unused signals
SIGUSR2. However, this means that you cannot use them in your program by any
means. They are setup by
vga_init() as everything else is.
Since version 1.2.11
vga_init() includes code to hunt for a free virtual console on its own in
case you are not starting the program from one (but instead over a network or
modem login, from within screen or an xterm). Provided there is a free
console, this succeeds if you are root or if the svgalib calling user own
the current console. This is to avoid people not using the console being able
to fiddle with it.
On graceful exit the program returns to the console from which it was started.
Otherwise it remains in text mode at the VC which svgalib allocated to allow
you to see any error messages. In any case, any I/O the svgalib makes in
text mode (after calling vga_init) will also take place at this new console.
Alas, some games misuse their suid root priviledge and run as full root
process. svgalib cannot detect this and allows Joe Blow User to open a new
VC on the console. If this annoys you
you to disable allocating a new VC for root (except when he owns the current
console) when compiling svgalib. This is the default (disabling the allocation for root).
vga_init() returns a non-zero value in case of errors. As of this writing it will return
-1 if it is unable to allocate a graphical console. Otherwise, 0 is returned.
Svgalib versions prior to 1.2.11 had a security hole where it would be possible
to regain root priviledges even after a
vga_init() call. This is not necessarily a problem, but if your program is vulnerable to
buffer overflows and other attacks, an attacker may exploit this.
However, prior to your call, your program will need to run setuid root, so you should
be very careful. The ioperm library by Olaf Titz will allow svgalib programs to run
not setuid root. However, it gives all programs unlimited access to the hardware. Again,
a malicious person can exploit this (albeit a bit more difficult) too.
Thus, in general, make your svgalib programs as secure as any setuid root program.
Some programs may (accidently) rely on the old behaviour (which was probably due to the
author not knowing about saved uids (which might actually even not have existed in Linux at that
time)). A line:
in the configuration file
/etc/vga/libvga.conf will reinstate the old behaviour whereas
enables the (currently default) action.
This manual page was edited by Michael Weller <firstname.lastname@example.org>. The
exact source of the referenced function as well as of the original documentation is
It is very likely that both are at least to some extent are due to
Harm Hanemaayer <H.Hanemaayer@inter.nl.net>.
Occasionally this might be wrong. I hereby
asked to be excused by the original author and will happily accept any additions or corrections
to this first version of the svgalib manual.
|Svgalib (>= 1.2.11) ||VGA_INIT (3) ||27 July 1997 |
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