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POWriting a file to a USB stick in linux with Python?
 

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  1. POWriting a file to a USB stick in linux with Python?
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    <p>I'm having a lot more trouble than expected writing to a file than I expected. I have a small Single Board computer running on an arm processor with the Angstrom embedded distribution. I'm writing an application for it with python. The application should detect the USB stick and then dump the file to it. The issue I'm running into is that even when my script appears to write the file correctly, and the file appears to be there using "ls" and "cat" in Linux, when I remove the USB stick and try to look at the file in Windows or another linux distro it's empty or more often not there at all. My application is multithreaded. I create /media/mymntpnt as root (directory.)</p> <p>Any help is appreciated.</p> <p>Here are some snippets of my code:</p> <p>This part is what I use to identify the USB stick:</p> <pre><code>class MediaScanner(): def __init__(self): self.lok = thread.allocate_lock() self.running = True self.started = False def register_cb(self,func): self.cb = func def start(self): if not self.started: thread.start_new_thread(self.scan_thread,()) def scan_thread(self): self.quit = False self.started = True last_devices = [] while self.running: devices = self.scan_media() if (devices != last_devices): self.cb(devices) #call the callback as its own thread last_devices = devices time.sleep(0.1) self.quit = True def stop(self): self.running = False while(not self.quit): pass return True def is_running(self): return self.running def scan_media(self): with self.lok: partitionsFile = open("/proc/partitions") lines = partitionsFile.readlines()[2:]#Skips the header lines devices = [] for line in lines: words = [x.strip() for x in line.split()] minorNumber = int(words[1]) deviceName = words[3] if minorNumber % 16 == 0: path = "/sys/class/block/" + deviceName if os.path.islink(path): if os.path.realpath(path).find("/usb") &gt; 0: devices.append('/dev/'+deviceName) partitionsFile.close() return devices </code></pre> <p>And here's an example of my script to write the file:</p> <pre><code>from mediascanner import * from util import * from database import * from log import * ms = MediaScanner() devices = ms.scan_media() print devices if devices: db = TestDatabase(init_tables=False) data = db.get_all_test_data() for device in devices: print device mount_partition(get_partition(device)) write_and_verify('/media/mymntpnt/test_'+get_log_file_name(),flatten_tests(data)) unmount_partition() </code></pre> <p>And here are my utility functions:</p> <pre><code>def write_and_verify(f_n,data): f = file(f_n,'w') f.write(data) f.flush() f.close() f = file(f_n,'r') verified = f.read() f.close() return verified == data and f.closed def get_partition(dev): os.system('fdisk -l %s &gt; output' % dev) f = file('output') data = f.read() print data f.close() return data.split('\n')[-2].split()[0].strip() def mount_partition(partition): os.system('mount %s /media/mymntpnt' % partition) def unmount_partition(): os.system('umount /media/mymntpnt') </code></pre>
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    1. COhave you tried `sync` and/or `pmount` and `pumount`? Kind of just brainstorming.
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    2. COalso look at `os.fdatasync` (probably amounts to something like `os.system('fsync ...)` on linux)
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    3. COso sometimes you do see the file on your computer?
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      1. UScwoebker
 

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