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  • boot issues - long delay, then "gave up waiting for root device"

    - by chazomaticus
    I've had this issue on and off for about two years now. I noticed it on a new (custom built) machine running 10.04 when that first came out, but then it went away until a few months ago. I've gone through a number of hard drive changes but I can't say specifically what if anything I changed hardware-wise to make it stop or start happening. I had assumed upgrading to a modern Ubuntu version would fix the issue, so I installed 12.04 beta on a spare partition last night, but it's still happening. Here's the issue. After grub loads and I select a kernel to boot, the screen goes blank save for a blinking cursor. It sits in this state for many long minutes before it finally gives up and gives me an initramfs shell with the message gave up waiting for root device (and lists the /dev/disk/by-uuid/... path it was waiting for) but no other specific diagnostic information. Now, here's the tricky part. For one, the problem is intermittent - sometimes it progresses from the blinking cursor to the Ubuntu splash boot screen in a few seconds, and once it gets that far it always continues booting fine. The really bizarre thing is that I can "force" it to "find" the root device by repeatedly pressing the space bar and hitting the machine's power button. If I tap those enough, eventually I will notice the hard drive light coming on, at which point it will always continue the boot process after a few seconds. Interestingly, if I wait slightly too long before pressing the power button (30s?), as soon as I press it I get the gave up waiting message and the initramfs shell. I've tried setting up /etc/fstab (and the grub menu.lst or whatever it's called nowadays) to use device names (e.g. /dev/sda1) instead of UUIDs, but I get the same effect just with the device name, not UUID, in the error message. I should also mention that when I boot to Windows 7, there is no issue. It boots slowly all the time just by virtue of being Windows, but it never hangs indefinitely. This would seem to indicate it's a problem in Ubuntu, not the hardware. It's pretty annoying to have to babysit the computer every time it boots. Any ideas? I'm at a loss. Not even sure how to diagnose the issue. Thanks! EDIT: Here's some dmesg output from 10.04. The 15 second gap is where it was doing nothing. I pressed the power button and space bar a few times, and the stuff at 16 seconds happened. Not sure what any of it means. [ 1.320250] scsi18 : ahci [ 1.320294] scsi19 : ahci [ 1.320320] ata19: SATA max UDMA/133 abar m8192@0xfd4fe000 port 0xfd4fe100 ir q 18 [ 1.320323] ata20: SATA max UDMA/133 abar m8192@0xfd4fe000 port 0xfd4fe180 ir q 18 [ 1.403886] usb 2-4: new high speed USB device using ehci_hcd and address 4 [ 1.562558] usb 2-4: configuration #1 chosen from 1 choice [ 16.477824] ata16: SATA link down (SStatus 0 SControl 300) [ 16.477843] ata19: SATA link down (SStatus 0 SControl 300) [ 16.477857] ata3: SATA link down (SStatus 0 SControl 300) [ 16.477895] ata15: SATA link down (SStatus 0 SControl 300) [ 16.477906] ata20: SATA link down (SStatus 0 SControl 300) [ 16.477977] ata17: SATA link down (SStatus 0 SControl 300) [ 16.478003] ata12: SATA link down (SStatus 0 SControl 300) [ 16.478046] ata13: SATA link down (SStatus 0 SControl 300) [ 16.478063] ata14: SATA link down (SStatus 0 SControl 300) [ 16.478108] ata11: SATA link down (SStatus 0 SControl 300) [ 16.478123] ata18: SATA link up 1.5 Gbps (SStatus 113 SControl 300) [ 16.478127] ata6: SATA link down (SStatus 0 SControl 300) [ 16.478157] ata5: SATA link down (SStatus 0 SControl 300) [ 16.478193] ata18.00: ATAPI: MARVELL VIRTUALL, 1.09, max UDMA/66 After that, it took its sweet time, and I had to keep hitting space bar to coax it along. Here's some more dmesg output from a little later in the boot process: [ 17.982291] input: BTC USB Multimedia Keyboard as /devices/pci0000:00/0000:00 :13.0/usb5/5-2/5-2:1.0/input/input4 [ 17.982335] generic-usb 0003:046E:5506.0002: input,hidraw1: USB HID v1.10 Key board [BTC USB Multimedia Keyboard] on usb-0000:00:13.0-2/input0 [ 18.005211] input: BTC USB Multimedia Keyboard as /devices/pci0000:00/0000:00 :13.0/usb5/5-2/5-2:1.1/input/input5 [ 18.005274] generic-usb 0003:046E:5506.0003: input,hiddev96,hidraw2: USB HID v1.10 Device [BTC USB Multimedia Keyboard] on usb-0000:00:13.0-2/input1 [ 22.484906] EXT4-fs (sda6): INFO: recovery required on readonly filesystem [ 22.484910] EXT4-fs (sda6): write access will be enabled during recovery [ 22.548542] EXT4-fs (sda6): recovery complete [ 22.549074] EXT4-fs (sda6): mounted filesystem with ordered data mode [ 32.516772] Adding 20482832k swap on /dev/sda5. Priority:-1 extents:1 across:20482832k [ 32.742540] udev: starting version 151 [ 33.002004] Bluetooth: Atheros AR30xx firmware driver ver 1.0 [ 33.008135] parport_pc 00:09: reported by Plug and Play ACPI [ 33.008186] parport0: PC-style at 0x378, irq 7 [PCSPP,TRISTATE] [ 33.012076] lp: driver loaded but no devices found [ 33.037271] ppdev: user-space parallel port driver [ 33.090256] lp0: using parport0 (interrupt-driven). Any clues in there?

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  • How can I properly create /dev/dvd?

    - by chazomaticus
    Certain programs look for /dev/dvd by default to find DVDs. When I first boot my computer without a DVD inserted, /dev/dvd exists and points to the correct place (/dev/sr0). However, when I insert a DVD, /dev/dvd disappears. I'd like it to stick around so I don't have to navigate to /dev/sr0 in programs that are looking for DVDs. How do I ensure that the /dev/dvd symlink exists and points to the right place? It looks like I can add something to /etc/udev/rules.d/70-persistent-cd.rules. This site gives a couple of examples, but the 70-persistent-cd.rules file says "add the ENV{GENERATED}=1 flag to your own rules", which isn't part of the examples. The man 7 udev page is impenetrable to me, and I'm not convinced the linked page gives 100% of the information I need. So, what can I do on a modern, Ubuntu 12.04 (or later) system to make /dev/dvd always exist and point to the right device? EDIT: Is it as simple as adding ENV{GENERATED}=1 to the rules in the linked page, something like this: SUBSYSTEM=="block", KERNEL=="sr0", SYMLINK+="dvd", GROUP="cdrom", ENV{GENERATED}=1 Is that the right information for modern Ubuntu? What is ENV{GENERATED} doing there, when it wasn't generated, but hand-written?

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  • Best way to test for a variable's existence in PHP; isset() is clearly broken

    - by chazomaticus
    From the isset() docs: isset() will return FALSE if testing a variable that has been set to NULL. Basically, isset() doesn't check for whether the variable is set at all, but whether it's set to anything but NULL. Given that, what's the best way to actually check for the existence of a variable? I tried something like: if(isset($v) || @is_null($v)) (the @ is necessary to avoid the warning when $v is not set) but is_null() has a similar problem to isset(): it returns TRUE on unset variables! It also appears that: @($v === NULL) works exactly like @is_null($v), so that's out, too. How are we supposed to reliably check for the existence of a variable in PHP? Edit: there is clearly a difference in PHP between variables that are not set, and variables that are set to NULL: <?php $a = array('b' => NULL); var_dump($a); PHP shows that $a['b'] exists, and has a NULL value. If you add: var_dump(isset($a['b'])); var_dump(isset($a['c'])); you can see the ambiguity I'm talking about with the isset() function. Here's the output of all three of these var_dump()s: array(1) { ["b"]=> NULL } bool(false) bool(false) Further edit: two things. One, a use case. An array being turned into the data of an SQL UPDATE statement, where the array's keys are the table's columns, and the array's values are the values to be applied to each column. Any of the table's columns can hold a NULL value, signified by passing a NULL value in the array. You need a way to differentiate between an array key not existing, and an array's value being set to NULL; that's the difference between not updating the column's value and updating the column's value to NULL. Second, Zoredache's answer, array_key_exists() works correctly, for my above use case and for any global variables: <?php $a = NULL; var_dump(array_key_exists('a', $GLOBALS)); var_dump(array_key_exists('b', $GLOBALS)); outputs: bool(true) bool(false) Since that properly handles just about everywhere I can see there being any ambiguity between variables that don't exist and variables that are set to NULL, I'm calling array_key_exists() the official easiest way in PHP to truly check for the existence of a variable. (Only other case I can think of is for class properties, for which there's property_exists(), which, according to its docs, works similarly to array_key_exists() in that it properly distinguishes between not being set and being set to NULL.)

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