Svgalib catches a bunch of signals that usually kill your program to restore textmode. If you catch signal's before calling vga_init() svgalib will restore textmode and prepare for shutdown and then call your handler routine. If you don't want this, catch the signal after calling vga_init and do not daisychain to svgalib's original handler.
WARNING! svgalib needs two signals for it's own purposes (that is managing console switches). To avoid problems it uses the otherwise unused signals SIGUSR1 and 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 ROOT_VC_SHORTCUT in Makefile.cfg allows 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.
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.
svgalib(7), vga_setmode(3), mouse_init(3), vga_claimvideomemory(3), vga_ext_set(3), vga_fillblt(3), vga_getcurrentchipset(3), vga_getdefaultmode(3), vga_getgraphmem(3), vga_runinbackground(3), vga_runinbackground_version(3), vga_safety_fork(3), vga_setchipset(3), vga_setchipsetandfeatures(3), vgagl(7), libvga.config(5),
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 unknown.
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.