blob: 0fad6600aa4d348c7bfd6d971d08c855b132d42c [file] [log] [blame]
/* vi: set sw=4 ts=4: */
* setlogcons: Send kernel messages to the current console or to console N
* Copyright (C) 2006 by Jan Kiszka <>
* Based on setlogcons (kbd-1.12) by Andries E. Brouwer
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
//config:config SETLOGCONS
//config: bool "setlogcons (1.8 kb)"
//config: default y
//config: select PLATFORM_LINUX
//config: help
//config: This program redirects the output console of kernel messages.
//applet:IF_SETLOGCONS(APPLET_NOEXEC(setlogcons, setlogcons, BB_DIR_USR_SBIN, BB_SUID_DROP, setlogcons))
//kbuild:lib-$(CONFIG_SETLOGCONS) += setlogcons.o
//usage:#define setlogcons_trivial_usage
//usage: "[N]"
//usage:#define setlogcons_full_usage "\n\n"
//usage: "Pin kernel output to VT console N. Default:0 (do not pin)"
// Comment from kernel source:
/* ...
* By default, the kernel messages are always printed on the current virtual
* console. However, the user may modify that default with the
* This function sets the kernel message console to be @new. It returns the old
* virtual console number. The virtual terminal number 0 (both as parameter and
* return value) means no redirection (i.e. always printed on the currently
* active console).
#include "libbb.h"
int setlogcons_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int setlogcons_main(int argc UNUSED_PARAM, char **argv)
char *devname;
struct {
char fn;
char subarg;
} arg = {
11, /* redirect kernel messages (TIOCL_SETKMSGREDIRECT) */
if (argv[1])
arg.subarg = xatou_range(argv[1], 0, 63);
/* Can just call it on "/dev/tty1" always, but...
* in my testing, inactive (never opened) VTs are not
* redirected to, despite ioctl not failing.
* By using "/dev/ttyN", ensure it is activated.
devname = xasprintf("/dev/tty%u", arg.subarg);
xioctl(xopen(devname, O_RDONLY), TIOCLINUX, &arg);