Comment 0 for bug 1817738

sudo strace chvt 4
execve("/bin/chvt", ["chvt", "4"], 0x7ffd63e5c758 /* 17 vars */) = 0
brk(NULL) = 0x561e18430000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=74655, ...}) = 0
mmap(NULL, 74655, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f5059e7d000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\34\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=2030544, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5059e7b000
mmap(NULL, 4131552, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f5059878000
mprotect(0x7f5059a5f000, 2097152, PROT_NONE) = 0
mmap(0x7f5059c5f000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1e7000) = 0x7f5059c5f000
mmap(0x7f5059c65000, 15072, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f5059c65000
close(3) = 0
arch_prctl(ARCH_SET_FS, 0x7f5059e7c500) = 0
mprotect(0x7f5059c5f000, 16384, PROT_READ) = 0
mprotect(0x561e17e87000, 4096, PROT_READ) = 0
mprotect(0x7f5059e90000, 4096, PROT_READ) = 0
munmap(0x7f5059e7d000, 74655) = 0
brk(NULL) = 0x561e18430000
brk(0x561e18451000) = 0x561e18451000
openat(AT_FDCWD, "/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=10281936, ...}) = 0
mmap(NULL, 10281936, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f5058ea9000
close(3) = 0
openat(AT_FDCWD, "/proc/self/fd/0", O_RDWR) = 3
ioctl(3, TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7ffdcdb0efa7) = -1 ENOTTY (Inappropriate ioctl for device)
close(3) = 0
openat(AT_FDCWD, "/dev/tty", O_RDWR) = 3
ioctl(3, TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7ffdcdb0efa7) = -1 ENOTTY (Inappropriate ioctl for device)
close(3) = 0
openat(AT_FDCWD, "/dev/tty0", O_RDWR) = 3
ioctl(3, TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7ffdcdb0efa7) = 0
ioctl(3, VT_ACTIVATE, 0x4) = 0
ioctl(3, VT_WAITACTIVE, 0x4

VT_ACTIVATE will cause a switch to VT number.
VT_WAITACTIVE will sleep/wait until the specified VT has been activated.

$ sudo cat /proc/$(pidof chvt)/stack
[<0>] __vt_event_wait.isra.2.part.3+0x40/0x90
[<0>] vt_waitactive+0x80/0xd0
[<0>] vt_ioctl+0xd26/0x1140
[<0>] tty_ioctl+0xf6/0x8c0
[<0>] do_vfs_ioctl+0xa8/0x630
[<0>] SyS_ioctl+0x79/0x90
[<0>] do_syscall_64+0x73/0x130
[<0>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[<0>] 0xffffffffffffffff