I have a 45-ish-gig virtual drive connected to a VM as my root partition.   root@alang-web:~# df -h Filesystem        Size  Used Avail Use% Mounted on udev              2.0G     0  2.0G   0% /dev tmpfs             396M  5.6M  390M   2% /run /dev/sda1          46G   41G  2.3G  95% / tmpfs             2.0G     0  2.0G   0% /dev/shm tmpfs             5.0M     0  5.0M   0% /run/lock tmpfs             2.0G     0  2.0G   0% /sys/fs/cgroup /dev/sdb1         148G   15G  126G  11% /mnt/data cgmfs             100K     0  100K   0% /run/cgmanager/fs alang-web-backup  621G  256G  366G  42% /media/sf_alang-web-backup tmpfs             396M     0  396M   0% /run/user/1000   As you can see, it reports 41 gigs of 46 gigs used.  And then there's this:  root@alang-web:~# du -shx / 27G /   And this:  root@alang-web:~# tune2fs -l /dev/sda1 tune2fs 1.42.13 (17-May-2015) ... Block count:              12058624 Reserved block count:     602931 Free blocks:              1209455 ...   And going to init 1 and running a fsck -f / reports no errors of any kind.  Where the heck is that 41G - 27G = 14G of space that is supposedly being used but is not visible to du? It can't be doubly-hard-linked files, that would cause du to be HIGHER than df (and anyway I don't know what would be doing that). It can't be unlinked files that are still in use, I have rebooted multiple times and the numbers simply don't change much. Also there's this:  COMMAND    PID     USER   FD   TYPE DEVICE SIZE/OFF NLINK    NODE NAME php-fpm7.  992     root    3u   REG    8,1        0     0 1837559 /tmp/.ZendSem.dSWbfL (deleted) mysqld    1020    mysql    4u   REG    8,1        0     0 1837551 /tmp/ibybXrs3 (deleted) mysqld    1020    mysql    5u   REG    8,1        0     0 1837623 /tmp/ibVK2BUX (deleted) mysqld    1020    mysql    6u   REG    8,1        0     0 1837628 /tmp/ibavDMmS (deleted) mysqld    1020    mysql    7u   REG    8,1        0     0 1837629 /tmp/ib5MSHjH (deleted) mysqld    1020    mysql   11u   REG    8,1        0     0 1837631 /tmp/ibf8ZvTB (deleted) php-fpm7. 1067 www-data    3u   REG    8,1        0     0 1837559 /tmp/.ZendSem.dSWbfL (deleted) php-fpm7. 1068 www-data    3u   REG    8,1        0     0 1837559 /tmp/.ZendSem.dSWbfL (deleted) apache2   1088     root   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted) apache2   1091 www-data   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted) apache2   1092 www-data   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted) apache2   1093 www-data   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted) apache2   1094 www-data   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted) apache2   1095 www-data   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted) apache2   1275 www-data   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted) apache2   1277 www-data   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted) apache2   1278 www-data   40u   REG    8,1        0     0 1837632 /tmp/.ZendSem.3m0mZe (deleted)   Those are all the unlinked files that it lists for that file system currently. I don't know how big those are (perhaps the size is inaccurate for files that are unlinked, or perhaps those really are size-0 files that are being used for semaphores or something of the sort.) However, it seems kind of unlikely that they're 14 gigs.  Is there some subtlety of ext4 that I don't know about? I freely admit to being more familiar with ext3 and HFS+. Is this somehow sharing space with some other partition or something like that, and the command line tool df hasn't kept up with modern times? Is the drive just broken in a way fsck can't even detect, let alone fix?  Just to preempt one other suggestion:  root@alang-web:~# cat &gt; /tmp/blar adsf root@alang-web:~# du -sh /tmp/* 4.0K    /tmp/blar root@alang-web:~#    So no, du does not report actual file sizes, it reports the size on disk including padding out to the next largest block size.
I have a SCSI disk in a server (hardware Raid 1), 32G, ext3 filesytem. df tells me that the disk is 100% full. If I delete 1G this is correctly shown.  However, if I run a du -h -x / then du tells me that only 12G are used (I use -x because of some Samba mounts).  So my question is not about subtle differences between the du and df commands but about how I can find out what causes this huge difference?  I rebooted the machine for a fsck that went w/out errors. Should I run badblocks? lsof shows me no open deleted files, lost+found is empty and there is no obvious warn/err/fail statement in the messages file.  Feel free to ask for further details of the setup.
Computing matrix-vector calculus derivatives $x, a$ in $\mathbb R^n$, $A$ in $\mathbb  R^{n\times n}$. Compute $d(x^T a)/dx$ and $d(x^T A x)/dx$.  I'm not sure about how to think about these and how to do these. Can someone explain how to derive the expressions for the two?  Finally, what happens when we have $A$ and $X$, BOTH in $\mathbb R^{n\times n}$, and we want to find $dTrace(XA)/dX$? Maintenance plan for creating transaction log backups I have a database that is set to the 'Full' recovery model, and I'm creating a maintenance plan to backup the Transaction Log every 15 minutes. A full backup is then taken once every 24 hours.  I was wondering: will the maintenance plan for the transaction logs create a lot of different files every 15 minutes, or will it by default append to the same file for 24 hours?  Also: what is preferred? I couldn't find anything on this subject (or maybe I was Googling the wrong words).  Thanks for any pointers anyone can give me.  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Immediately, his insides started writhing as though he'd just swallowed live snakes -- doubled up, he wondered whether he was going to be sick -- then a burning sensation spread rapidly form his stomach to the very ends of his fingers and toes -- next, bringing him gasping to all fours, came to a horrible melting feeling, as the skin all over his body bubbled like hot wax -- and before their eyes, his hands began to grow, the fingers thickened, the knuckles were bulging like bolts -- his shoulders stretched painfully and a prickling on his forehead told him that his hair was creeping down toward his eyebrows -- his robes ripped as his chest expanded like a barrel bursting its hoops -- his feet were agony in shoes four sizes too small      Harry potter and the chamber of secrets   It is the description of the feeling of drinking Polyjuice Potion, which makes someone into a different person, from the point of view of Harry Potter turning into Gregory Goyle.  And I don't understand what 'bring him gasping to all fours' means, especially 'four'. Does four here mean number 4? How do I restart the SSH service? Trigger Setup Wizard at next boot using command-line I am looking for a way to use ADB to trigger Setup Wizard at next boot. I know I can run the following command and get it to pop up. However, I can't figure out what triggers it to start at boot.  adb shell am start -a android.intent.action.MAIN -n com.google.android.setupwizard/.SetupWizardTestActivity   The phone I am currently using is stock and I would like to keep it that way.   I've read the  question: I want to turn my system on automatically every day. So I use the below code in my Python script, but sudo asks me for a password every time:  os.system('sudo sh -c "echo date \'+%s\' -d \'+ \        24 hours\' &gt; /sys/class/rtc/rtc0/wakealarm"')   How can I run this script without sudo asking for the password every time? 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For example (just an example of how it should be):   for iterating an array of 1000+ strings - for is better than foreach for iterating over IList (non generic) strings - foreach is better than for   A few references found on the web for the same:               [Edit]  Apart from the readability aspect of it, I am really interested in facts and figures. There are applications where the last mile of performance optimization squeezed do matter. Someone who just thinks they know what they're talking about Can I use the Adwaita theme in Unity without installing GNOME shell? I recently installed Ubuntu 11.10 (new install). I would like to use the Adwaita theme with Unity, but it seems that it is not available in the theme selection dialog. I know I get it there after installing gnome-shell, but is there a way to use Adwaita theme for Unity without installing gnome-shell? 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