You can do this using udisks. It is not installed by default, but it is easy enough to install (the package is like a megabyte in size once installed)...

    sudo apt-get install udisks

Once installed, you can detach a USB drive with the following commands...

    sudo udisks --unmount /dev/sdb1
    sudo udisks --detach /dev/sdb

The first line unmounts it. Just like any other partition you can still remount it at this point. The second line detaches it. After this it is powered down and you have to remove/reinsert it to remount.

To clarify, *sdb* is the device and *sdb1*, *sdb2*, *sdb3*, etc. are partitions on the device. Also, you will need to unmount all mount points before you attempt to detach the device. Usually with a USB stick/drive there is only one but it is a warning you should know about none the less.

Getting the device name from the mount point would require you pull it from mount or something.






I&#39;m designing an API with SQLAlchemy (querying MySQL) and I would like to force all my queries to have page_size (LIMIT) and page_number (OFFSET) parameters.

Is there a clean way of doing this with SQLAlchemy?  Perhaps building a factory of some sort to create a custom Query object?  Or maybe there is a good way to do this with a mixin class?

I tried the obvious thing and it didn&#39;t work because .limit() and .offset() must be called after all filter conditions have been applied:

    def q(page=0, page_size=None):
        q = session.query(...)
        if page_size: q = q.limit(page_size)
        if page: q = q.offset(page*page_size)
        return q

When I try using this, I get the exception:

    sqlalchemy.exc.InvalidRequestError: Query.filter() being called on a Query which already has LIMIT or OFFSET applied. To modify the row-limited results of a  Query, call from_self() first.  Otherwise, call filter() before limit() or offset() are applied.


Applying LIMIT and OFFSET to all queries in SQLAlchemy

`java.io.IOException` seems to be the most common type of exception, and coincidentally, it seems to also be the most ambiguous.

I keep seeing the `throws IOException` whenever writing with sockets, files, etc. I&#39;ve never actually had one fired on me, however, so I&#39;m wondering what it is that is supposed to fire the exception. The documentation isn&#39;t very helpful in explaining what&#39;s going on: 

&gt; Signals that an I/O exception of some sort has occurred. This class is the general class of exceptions produced by failed or interrupted I/O operations.

What are some instances where an IOException would be thrown, and how is it supposed to be used?



What throws an IOException in Java?

It would just be cool if your shell script helps you to **safely remove your flash disk** after finishing its job. The solution is expected to meet the following needs:

 1. Suppose the flash disk is mounted as `/media/A` together with many other flash disks and the code can selectively just remove `/media/A` without interfering other disks. For example, I can pass `/media/A` as an argument.
 2. A light solution. Installing another package of size 100MB to finish the task drives one crazy.
 3. I know some commands like `hdparm` except their documents are hard to read. If one can offer me a solution I hope he/she can offer also the explanation of the parameters, etc.
 4. Best if the code can handle all kinds of flash disks (for example, my old one bought in 2003 with 32&amp;nbsp;MB) (and portable disks optionally).
 5. It should achieve the exact effect as right clicking the disk &amp;rarr; clicking &quot;safely Remove Drive&quot;. The safety concern will prevail, otherwise one may just unplug the disk which usually won&#39;t hurt.



Linux (Ubuntu): safely remove a USB flash disk via the command line

<p>It would just be cool if your shell script helps you to <strong>safely remove your flash disk</strong> after finishing its job. The solution is expected to meet the following needs:</p>
<ol>
<li>Suppose the flash disk is mounted as <code>/media/A</code> together with many other flash disks and the code can selectively just remove <code>/media/A</code> without interfering other disks. For example, I can pass <code>/media/A</code> as an argument.</li>
<li>A light solution. Installing another package of size 100MB to finish the task drives one crazy.</li>
<li>I know some commands like <code>hdparm</code> except their documents are hard to read. If one can offer me a solution I hope he/she can offer also the explanation of the parameters, etc.</li>
<li>Best if the code can handle all kinds of flash disks (for example, my old one bought in 2003 with 32 MB) (and portable disks optionally).</li>
<li>It should achieve the exact effect as right clicking the disk → clicking "safely Remove Drive". The safety concern will prevail, otherwise one may just unplug the disk which usually won't hurt.</li>
</ol>


Here is how the error output is if I run `virtualbox` from the terminal. How to correct it? I am on a Ubuntu 12.10 64bit machine.

    virtualbox
    WARNING: The character device /dev/vboxdrv does not exist.
    	 Please install the virtualbox-ose-dkms package and the appropriate
    	 headers, most likely linux-headers-generic.
    
    	 You will not be able to start VMs until this problem is fixed.

EDIT:

I have both the latest `linux-headers-generic` and `virtualbox-ose-dkms` packages

How to correct virtualbox installation

In the windows environment you will have .m2 folder in C:\Users\user_name location and you will copy your settings.xml file to it in order to setup your proxy settings and nexus repository locations and etc.

So What I have to done on Ubuntu environment to get similar setup after installing maven on it. 

.m2 , settings.xml in Ubuntu

Is it possible in Linux command line to have a command repeat every *n* seconds?

Say, I have an import running, and I am doing

    ls -l

to check if the file size is increasing. I would like to have a command to have this repeat automatically.

Repeat command automatically in Linux

I used the following command to convert and merge all the `jpg` files in a directory to a single pdf file.

    convert *.jpg file.pdf

The files in the directory are numbered from `1.jpg` to `123.jpg`. The convertion went fine but after converting the pages were all mixed up. I wanted the pdf to have pages from `1.jpg` to `123.jpg` in the same order as they are named. I tried with the following command as well:

    cd 1 
    FILES=$( find . -type f -name &quot;*jpg&quot; | cut -d/ -f 2)
    mkdir temp &amp;&amp; cd temp 
    for file in $FILES; do 
        BASE=$(echo $file | sed &#39;s/.jpg//g&#39;);
        convert ../$BASE.jpg $BASE.pdf; 
        done &amp;&amp; 
    pdftk *pdf cat output ../1.pdf &amp;&amp; 
    cd .. 
    rm -rf temp

But still no luck. Operating platform Linux.

Merge multiple jpg into single pdf in Linux

My Ubuntu computer had crashed, and when I restarted it MongoDB wasn&#39;t working. I tried the following commands, and got the following output:

    $ mongo
    Error: couldn&#39;t connect to server 127.0.0.1:27017 src/mongo/shell/mongo.js:91
    exception: connect failed

    $ service mongodb status
    mongodb stop/waiting

    $ service mongodb restart
    stop: Unknown instance: 
    start: Rejected send message, 1 matched rules; type=&quot;method_call&quot;,
           sender=&quot;:1.57&quot; (uid=1000 pid=2227 comm=&quot;start mongodb &quot;)
           interface=&quot;com.ubuntu.Upstart0_6.Job&quot; member=&quot;Start&quot; error name=&quot;(unset)&quot;
           requested_reply=&quot;0&quot;
           destination=&quot;com.ubuntu.Upstart&quot; (uid=0 pid=1 comm=&quot;/sbin/init&quot;)

    $ tail /var/log/mongodb/mongodb.log
    [initandlisten] exception in initAndListen: 12596 old lock file, terminating
    dbexit: 
    [initandlisten] shutdown: going to close listening sockets...
    [initandlisten] shutdown: going to flush diaglog...
    [initandlisten] shutdown: going to close sockets...
    [initandlisten] shutdown: waiting for fs preallocator...
    [initandlisten] shutdown: closing all files...
    [initandlisten] closeAllFiles() finished
    dbexit: really exiting now


(Output reformatted to match website layout.)

What happened? How can I fix it?

MongoDB won&#39;t start after server crash

I have an LG-E405 phone running Android 2.3.6.

I connected my phone with a USB cable and selected the mode as `Charge Only`.

Now when I try to turn on `USB Debugging`, I find that that the option is greyed out.

So, how can I enable USB debugging in this case.

USB Debugging option greyed out

This question seems to be all over google, but the answers all point to using System Profiler. That&#39;s nice, but with System Profiler all you get is something that looks like this:


                DasKeyboard:

                  Product ID: 0x1919
                  Vendor ID: 0x04d9  (Holtek Semiconductor, Inc.)
                  Version: 1.06
                  Speed: Up to 1.5 Mb/sec
                  Location ID: 0x1d114000 / 11
                  Current Available (mA): 500
                  Current Required (mA): 100

                USB2.0 Hub:

                  Product ID: 0x0608
                  Vendor ID: 0x05e3  (Genesys Logic, Inc.)
                  Version: 32.98
                  Speed: Up to 480 Mb/sec
                  Location ID: 0x1d113000 / 10
                  Current Available (mA): 500
                  Current Required (mA): 100

                    Microsoft Basic Optical Mouse v2.0 :

                      Product ID: 0x00cb
                      Vendor ID: 0x045e  (Microsoft Corporation)
                      Version: 1.99
                      Speed: Up to 1.5 Mb/sec
                      Manufacturer: Microsoft 
                      Location ID: 0x1d113200 / 12
                      Current Available (mA): 500
                      Current Required (mA): 100

That&#39;s great if all you want are the contents of a bunch of device descriptors, but `lsusb` gives you *so* much more - information on interfaces and endpoints, interface associations, composite devices... where can you find this information in OS X? There *must* be a tool that does this?


Is there an equivalent of lsusb for OS X

I have a USB device that reads data from a system and transfers them to the computer. I am wondering if it&#39;s possible to have a Linux single board PC (i.e. Raspberry Pi) to run a script and be a remote-server for my USB device and I can connect to that &quot;remote-server&quot;(Linux) through SSH or FTP or another protocol (over the Internet) and mount that USB port to my computer. Any software would do it, you know how terminal service connects the remote resources, and I need the same, but preferably on a Linux board.

My system is Windows&amp;nbsp;7, so I need to mount that remote-USB as a &quot;local port&quot; so the software thinks it&#39;s communicating locally, and it&#39;ll find the reader.


Using a remote host&#39;s USB port as local USB (Linux and Windows)

I&#39;m trying to get some data out of a USB device connected to my Android phone that is on host mode. I&#39;m able to send data to it, but reading fails.

I&#39;ve looked at [several][1] [examples][2] and tried all I could but I don&#39;t have any experience in USB communication, although by now I know a little, and I&#39;ve been stuck on this longer that I care to admit.

I&#39;m not very familiar with the endpoint configuration, but I know is that my device uses a CDC type communication method and both the output (from phone to device) and input are registered.

Here&#39;s the whole class that manages the USB connection with the only device that is connected to the phone, it&#39;s not finished by any means, but I&#39;d like to get that reading part to work before I go any further.

    public class UsbCommunicationManager
    {
    	static final String ACTION_USB_PERMISSION = &quot;com.android.example.USB_PERMISSION&quot;;
    
    	UsbManager usbManager;
    	UsbDevice usbDevice;
    	UsbInterface intf = null;
    	UsbEndpoint input, output;
    	UsbDeviceConnection connection;
    
    	PendingIntent permissionIntent;
    
    	Context context;
    
    	byte[] readBytes = new byte[64];
    
    	public UsbCommunicationManager(Context context)
    	{
    		this.context = context;
    		usbManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
    
    		// ask permission from user to use the usb device
    		permissionIntent = PendingIntent.getBroadcast(context, 0, new Intent(ACTION_USB_PERMISSION), 0);
    		IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
    		context.registerReceiver(usbReceiver, filter);
    	}
    
    	public void connect()
    	{
    		// check if there&#39;s a connected usb device
    		if(usbManager.getDeviceList().isEmpty())
    		{
    			Log.d(&quot;trebla&quot;, &quot;No connected devices&quot;);
    			return;
    		}
    
    		// get the first (only) connected device
    		usbDevice = usbManager.getDeviceList().values().iterator().next();
    
    		// user must approve of connection
    		usbManager.requestPermission(usbDevice, permissionIntent);
    	}
    
    	public void stop()
    	{
    		context.unregisterReceiver(usbReceiver);
    	}
    
    	public String send(String data)
    	{
    		if(usbDevice == null)
    		{
    			return &quot;no usb device selected&quot;;
    		}
    
    		int sentBytes = 0;
    		if(!data.equals(&quot;&quot;))
    		{
    			synchronized(this)
    			{
    				// send data to usb device
    				byte[] bytes = data.getBytes();
    				sentBytes = connection.bulkTransfer(output, bytes, bytes.length, 1000);
    			}
    		}
    
    		return Integer.toString(sentBytes);
    	}
    
    	public String read()
    	{
    		// reinitialize read value byte array
    		Arrays.fill(readBytes, (byte) 0);
    
    		// wait for some data from the mcu
    		int recvBytes = connection.bulkTransfer(input, readBytes, readBytes.length, 3000);
    
    		if(recvBytes &gt; 0)
    		{
    			Log.d(&quot;trebla&quot;, &quot;Got some data: &quot; + new String(readBytes));
    		}
    		else
    		{
    			Log.d(&quot;trebla&quot;, &quot;Did not get any data: &quot; + recvBytes);
    		}
    
    		return Integer.toString(recvBytes);
    	}
    
    	public String listUsbDevices()
    	{
    		HashMap&lt;String, UsbDevice&gt; deviceList = usbManager.getDeviceList();
    
    		if(deviceList.size() == 0)
    		{
    			return &quot;no usb devices found&quot;;
    		}
    
    		Iterator&lt;UsbDevice&gt; deviceIterator = deviceList.values().iterator();
    		String returnValue = &quot;&quot;;
    		UsbInterface usbInterface;
    
    		while(deviceIterator.hasNext())
    		{
    			UsbDevice device = deviceIterator.next();
    			returnValue += &quot;Name: &quot; + device.getDeviceName();
    			returnValue += &quot;\nID: &quot; + device.getDeviceId();
    			returnValue += &quot;\nProtocol: &quot; + device.getDeviceProtocol();
    			returnValue += &quot;\nClass: &quot; + device.getDeviceClass();
    			returnValue += &quot;\nSubclass: &quot; + device.getDeviceSubclass();
    			returnValue += &quot;\nProduct ID: &quot; + device.getProductId();
    			returnValue += &quot;\nVendor ID: &quot; + device.getVendorId();
    			returnValue += &quot;\nInterface count: &quot; + device.getInterfaceCount();
    
    			for(int i = 0; i &lt; device.getInterfaceCount(); i++)
    			{
    				usbInterface = device.getInterface(i);
    				returnValue += &quot;\n  Interface &quot; + i;
    				returnValue += &quot;\n\tInterface ID: &quot; + usbInterface.getId();
    				returnValue += &quot;\n\tClass: &quot; + usbInterface.getInterfaceClass();
    				returnValue += &quot;\n\tProtocol: &quot; + usbInterface.getInterfaceProtocol();
    				returnValue += &quot;\n\tSubclass: &quot; + usbInterface.getInterfaceSubclass();
    				returnValue += &quot;\n\tEndpoint count: &quot; + usbInterface.getEndpointCount();
    
    				for(int j = 0; j &lt; usbInterface.getEndpointCount(); j++)
    				{
    					returnValue += &quot;\n\t  Endpoint &quot; + j;
    					returnValue += &quot;\n\t\tAddress: &quot; + usbInterface.getEndpoint(j).getAddress();
    					returnValue += &quot;\n\t\tAttributes: &quot; + usbInterface.getEndpoint(j).getAttributes();
    					returnValue += &quot;\n\t\tDirection: &quot; + usbInterface.getEndpoint(j).getDirection();
    					returnValue += &quot;\n\t\tNumber: &quot; + usbInterface.getEndpoint(j).getEndpointNumber();
    					returnValue += &quot;\n\t\tInterval: &quot; + usbInterface.getEndpoint(j).getInterval();
    					returnValue += &quot;\n\t\tType: &quot; + usbInterface.getEndpoint(j).getType();
    					returnValue += &quot;\n\t\tMax packet size: &quot; + usbInterface.getEndpoint(j).getMaxPacketSize();
    				}
    			}
    		}
    
    		return returnValue;
    	}
    
    	private void setupConnection()
    	{
    		// find the right interface
    		for(int i = 0; i &lt; usbDevice.getInterfaceCount(); i++)
    		{
    			// communications device class (CDC) type device
    			if(usbDevice.getInterface(i).getInterfaceClass() == UsbConstants.USB_CLASS_CDC_DATA)
    			{
    				intf = usbDevice.getInterface(i);
    
    				// find the endpoints
    				for(int j = 0; j &lt; intf.getEndpointCount(); j++)
    				{
    					if(intf.getEndpoint(j).getDirection() == UsbConstants.USB_DIR_OUT &amp;&amp; intf.getEndpoint(j).getType() == UsbConstants.USB_ENDPOINT_XFER_BULK)
    					{
    						// from android to device
    						output = intf.getEndpoint(j);
    					}
    
    					if(intf.getEndpoint(j).getDirection() == UsbConstants.USB_DIR_IN &amp;&amp; intf.getEndpoint(j).getType() == UsbConstants.USB_ENDPOINT_XFER_BULK)
    					{
    						// from device to android
    						input = intf.getEndpoint(j);
    					}
    				}
    			}
    		}
    	}
    
    	private final BroadcastReceiver usbReceiver = new BroadcastReceiver()
    	{
    		public void onReceive(Context context, Intent intent)
    		{
    			String action = intent.getAction();
    			if(ACTION_USB_PERMISSION.equals(action))
    			{
    				// broadcast is like an interrupt and works asynchronously with the class, it must be synced just in case
    				synchronized(this)
    				{
    					if(intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false))
    					{
    						setupConnection();
    
    						connection = usbManager.openDevice(usbDevice);
    						connection.claimInterface(intf, true);
    
    						// set flow control to 8N1 at 9600 baud
    						int baudRate = 9600;
    						byte stopBitsByte = 1;
    						byte parityBitesByte = 0;
    						byte dataBits = 8;
    						byte[] msg = {
    							(byte) (baudRate &amp; 0xff),
    							(byte) ((baudRate &gt;&gt; 8) &amp; 0xff),
    							(byte) ((baudRate &gt;&gt; 16) &amp; 0xff),
    							(byte) ((baudRate &gt;&gt; 24) &amp; 0xff),
    							stopBitsByte,
    							parityBitesByte,
    							(byte) dataBits
    						};
    
    						connection.controlTransfer(UsbConstants.USB_TYPE_CLASS | 0x01, 0x20, 0, 0, msg, msg.length, 5000);
    					}
    					else
    					{
    						Log.d(&quot;trebla&quot;, &quot;Permission denied for USB device&quot;);
    					}
    				}
    			}
    			else if(UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action))
    			{
    				Log.d(&quot;trebla&quot;, &quot;USB device detached&quot;);
    			}
    		}
    	};
    }

I keep getting `-1` from the `read()` method which indicates some kind of error, it always times out. Maybe the problem comes from the connection configuration, I&#39;ve tried several (read: trial and error) and none worked, surprisingly I don&#39;t need any configuration to send data to the device.

---

*Edit*

It must also be noted that the cable I&#39;m using is micro-USB to micro-USB and it only works in one way, that is my device is powered by my phone only when the plug A connected to phone and plug B connected to device, not the other way around... it seems very strange. The fact that I&#39;m able to send data and not receive when plugged the _right way_ remains.

---

*EDIT 2*

I found that [somebody else had the same problem][3] but it seems he wasn&#39;t able to solve it.

---

*EDIT 3*

I finally found the solution on [this page][4]:

&gt; Another major oversight is that there is no mechanism for the host to notify the device that there is a data sink on the host side ready to accept data. This means that the device may try to send data while the host isn&#39;t listening, causing lengthy blocking timeouts in the transmission routines. It is thus highly recommended that the virtual serial line DTR (Data Terminal Ready) signal be used where possible to determine if a host application is ready for data.

So the DTR signal was mandatory and all I had to do was to add this to the interface configuration:

    connection.controlTransfer(0x21, 0x22, 0x1, 0, null, 0, 0);


---

*EDIT 4*

If anybody is interested I finished the project and it&#39;s [open source and published on my GitHub account][5]. It&#39;s not stable all the time though (see the [notes][6]) and I don&#39;t plan working on it anymore, but it works. Feel free to use it for your own projects.


  [1]: https://github.com/mik3y/usb-serial-for-android
  [2]: https://github.com/ksksue/FTDriver
  [3]: http://www.basic4ppc.com/android/forum/threads/usb-to-arduino-only-working-in-one-direction.28569/
  [4]: http://www.fourwalledcubicle.com/files/LUFA/Doc/120730/html/group___group___u_s_b_class_c_d_c_device.html
  [5]: https://github.com/Nurgak/Smartphone-sensor-data-collection-application
  [6]: https://github.com/Nurgak/Smartphone-sensor-data-collection-application#notes

Android USB host read from device

I am encountering a problem with Android ADB debugging through USB.

Using Macbook Air 2013 and trying to connect Nexus 6 dev phone.

On the MAC Android Studio, android latest sdk is installed.

When I do 

    adb kill-server
    adb devices

I get:

    adb I   661  9881 usb_osx.cpp:259] Found vid=18d1 pid=**** serial=*****
    adb I   661  9881 usb_osx.cpp:259] 
    adb E   661  9881 usb_osx.cpp:331] Could not open interface: e00002c5
    adb E   661  9881 usb_osx.cpp:265] Could not find device interface

So it found the device, vendor id, product id and serial match what I find in the system information for the Nexus 6.

Following suggestions found online I tried - but no success - the following to resolve:

- dis- and reenabling debugging mode on the phone, also switching between USB configs for charging, MTP, PTP, RNDIS, Audio Source, MIDI, always making sure the authoriztation for the Mac&#39;s RSA fingerprint is given

- closing Android Studio / DDMS, killing adb through &#39;kill-server&#39; command as well as killing process through Apple activity monitor

- run adb as root

- reboot the Mac several times

- reboot the Nexus 6

- reinstall Android SDK completely

- tried with another debugging enabled Android Device (Samsung Galaxy Tab, also here adb found correct device info but cannot access interface with same error)

- tried with 3 different USB cables, all cables which were originally shipped with Android devices

Through google I learned that error code e00002c5 means the device is already in use by another driver. 

I had recently installed Sophos Home Antivir. Thinking that this might prevent ADB from opening the device interface, I uninstalled Sophos completely with the provided uninstaller and rebooted the Mac.

Any hint is appreciated: 

- which steps to resolve?

- as e00002c5 seems to be a clear indicator that another driver has the device in use, how to find out which process that is and how to stop it from doing that


Content Type	Original Author	Original Content on Stackoverflow
Question	user1539634	View Question on Stackoverflow
Solution 1 - Ubuntu	Omnikrys	View Answer on Stackoverflow

Linux (Ubuntu): safely remove a USB flash disk via the command line

Ubuntu Problem Overview

Ubuntu Solutions

Solution 1 - Ubuntu

What throws an IOException in Java?

Applying LIMIT and OFFSET to all queries in SQLAlchemy

Attributions