Python ctypes calling reboot() from libc on Linux

Question

I'm trying to call the reboot function from libc in Python via ctypes and I just can not get it to work. I've been referencing the man 2 reboot page (http://linux.die.net/man/2/reboot). My kernel version is 2.6.35.

Below is the console log from the interactive Python prompt where I'm trying to get my machine to reboot- what am I doing wrong?

Why isn't ctypes.get_errno() working?

>>> from ctypes import CDLL, get_errno
>>> libc = CDLL('libc.so.6')
>>> libc.reboot(0xfee1dead, 537993216, 0x1234567, 0)
-1
>>> get_errno()
0
>>> libc.reboot(0xfee1dead, 537993216, 0x1234567)
-1
>>> get_errno()
0
>>> from ctypes import c_uint32
>>> libc.reboot(c_uint32(0xfee1dead), c_uint32(672274793), c_uint32(0x1234567), c_uint32(0))
-1
>>> get_errno()
0
>>> libc.reboot(c_uint32(0xfee1dead), c_uint32(672274793), c_uint32(0x1234567))
-1
>>> get_errno()
0
>>>

Edit:

Via Nemos reminder- I can get get_errno to return 22 (invalid argument). Not a surprise. How should I be calling reboot()? I'm clearly not passing arguments the function expects. =)

access denied? I don't know... try (re)reading this: http://linux.die.net/man/2/reboot — Manux, Jun 01 '11 at 02:26
Even if access were denied, one would expect `errno` to report `EPERM`. — sarnold, Jun 01 '11 at 02:27

Nemo · Accepted Answer · 2011-06-01T03:52:12.563

4

Try:

>>> libc = CDLL('libc.so.6', use_errno=True)

That should allow get_errno() to work.

[update]

Also, the last argument is a void *. If this is a 64-bit system, then the integer 0 is not a valid repesentation for NULL. I would try None or maybe c_void_p(None). (Not sure how that could matter in this context, though.)

[update 2]

Apparently reboot(0x1234567) does the trick (see comments).

edited Jun 01 '11 at 03:52

answered Jun 01 '11 at 02:53

Nemo

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trying `libc.reboot(0xfee1dead, 672274793, 0x1234567, c_void_p(None))` still returns errno 22. thanks for the idea though. (so does trying to use `c_uint()` around the args) – tMC Jun 01 '11 at 03:11
Have you tried just `reboot(0x1234567)`? That's the signature I see in sys/reboot.h... – Nemo Jun 01 '11 at 03:19
I thought I had, but I guess not- that seems to do the trick. Maybe update the answer? – tMC Jun 01 '11 at 03:41

score 3 · Answer 2 · answered Jun 01 '11 at 03:45

The reboot() in libc is a wrapper around the syscall, which only takes the cmd argument. So try:

libc.reboot(0x1234567)

Note that you should normally be initiating a reboot by sending SIGINT to PID 1 - telling the kernel to reboot will not give any system daemons the chance to shut down cleanly, and won't even sync the filesystem cache to disk.

Python ctypes calling reboot() from libc on Linux

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