13

I am trying to write python script to find out if a disk device exists in /dev, but it always yield False. Any other way to do this?

I tried

>>> import os.path
>>> os.path.isfile("/dev/bsd0")
False
>>> os.path.exists("/dev/bsd0")
False

$ ll /dev
...
brw-rw----   1 root disk    252,   0 Nov 12 21:28 bsd0
...
electro
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2 Answers2

7

Some unconventional situation is going on here.

os.path.isfile() will return True for regular files, for device files this will be False.

But as for os.path.exists(), documetation states that False may be returned if "permission is not granted to execute os.stat()". FYI the implementation of os.path.exists is:

def exists(path):
    """Test whether a path exists.  Returns False for broken symbolic links"""
    try:
        os.stat(path)
    except OSError:
        return False
    return True

So, if os.stat is failing on you I don't see how ls could have succeeded (ls AFAIK also calls stat() syscall). So, check what os.stat('/dev/bsd0') is raising to understand why you're not being able to detect the existence of this particular device file with os.path.exists, because using os.path.exists() is supposed to be a valid method to check for the existence of a block device file.

jvdm
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5

This was not rigorously tested, but seems to work:

import stat
import os.stat

def disk_exists(path):
     try:
             return stat.S_ISBLK(os.stat(path).st_mode)
     except:
             return False

Results:

disk_exists("/dev/bsd0")
True
disk_exists("/dev/bsd2")
False
pgreen2
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