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• How can I back up my ubuntu system?

  - by Eloff

  I'm sure there's a lot of questions on here similar to this, and I've been reading them, but I still feel this warrants a new question. I want nightly, incremental backups (full disk images would waste a lot of space - unless compressed somehow.) Preferably rotating or deleting old backups when running out of space or after a fixed number of backups. I want to be able to quickly and painlessly restore my system from these backups. This is my first time running ubuntu as my main development machine and I know from my experience with it as a server and in virtual machines that I regularly manage to make it unbootable or damage it to the point of being unable to rescue it. So how would you recommend I do this? There are so many options out there I really don't know where to start. There seems to be a vocal school of thought that it's sufficient to backup your home directory and the list of installed packages from the package manager. I've already installed lots of things from source, or outside of the package manager (development tools, ides, compilers, graphics drivers, etc.) So at the very least, if I do not back up the operating system itself I need to grab all config files, all program binaries, all created but required files, etc. I'd rather backup too much than too little - an ubuntu install is tiny anyway. Also this drastically reduces the restore time, which would cost me more in my time than the extra storage space. I tried using Deja Dup to backup the root partition, excluding some things like /mnt /media /dev /proc etc. Although many websites assured me you can backup a running linux system this way - that seems to be false as it complained that it could not backup the following files: /boot/System.map-3.0.0-17-generic /boot/System.map-3.2.0-22-generic /boot/vmcoreinfo-3.0.0-17-generic /boot/vmlinuz-3.0.0-17-generic /boot/vmlinuz-3.2.0-22-generic /etc/.pwd.lock /etc/NetworkManager/system-connections/LAN Connection /etc/apparmor.d/cache/lightdm-guest-session /etc/apparmor.d/cache/sbin.dhclient /etc/apparmor.d/cache/usr.bin.evince /etc/apparmor.d/cache/usr.lib.telepathy /etc/apparmor.d/cache/usr.sbin.cupsd /etc/apparmor.d/cache/usr.sbin.tcpdump /etc/apt/trustdb.gpg /etc/at.deny /etc/ati/inst_path_default /etc/ati/inst_path_override /etc/chatscripts /etc/cups/ssl /etc/cups/subscriptions.conf /etc/cups/subscriptions.conf.O /etc/default/cacerts /etc/fuse.conf /etc/group- /etc/gshadow /etc/gshadow- /etc/mtab.fuselock /etc/passwd- /etc/ppp/chap-secrets /etc/ppp/pap-secrets /etc/ppp/peers /etc/security/opasswd /etc/shadow /etc/shadow- /etc/ssl/private /etc/sudoers /etc/sudoers.d/README /etc/ufw/after.rules /etc/ufw/after6.rules /etc/ufw/before.rules /etc/ufw/before6.rules /lib/ufw/user.rules /lib/ufw/user6.rules /lost+found /root /run/crond.reboot /run/cups/certs /run/lightdm /run/lock/whoopsie/lock /run/udisks /var/backups/group.bak /var/backups/gshadow.bak /var/backups/passwd.bak /var/backups/shadow.bak /var/cache/apt/archives/lock /var/cache/cups/job.cache /var/cache/cups/job.cache.O /var/cache/cups/ppds.dat /var/cache/debconf/passwords.dat /var/cache/ldconfig /var/cache/lightdm/dmrc /var/crash/_usr_lib_x86_64-linux-gnu_colord_colord.102.crash /var/lib/apt/lists/lock /var/lib/dpkg/lock /var/lib/dpkg/triggers/Lock /var/lib/lightdm /var/lib/mlocate/mlocate.db /var/lib/polkit-1 /var/lib/sudo /var/lib/urandom/random-seed /var/lib/ureadahead/pack /var/lib/ureadahead/run.pack /var/log/btmp /var/log/installer/casper.log /var/log/installer/debug /var/log/installer/partman /var/log/installer/syslog /var/log/installer/version /var/log/lightdm/lightdm.log /var/log/lightdm/x-0-greeter.log /var/log/lightdm/x-0.log /var/log/speech-dispatcher /var/log/upstart/alsa-restore.log /var/log/upstart/alsa-restore.log.1.gz /var/log/upstart/console-setup.log /var/log/upstart/console-setup.log.1.gz /var/log/upstart/container-detect.log /var/log/upstart/container-detect.log.1.gz /var/log/upstart/hybrid-gfx.log /var/log/upstart/hybrid-gfx.log.1.gz /var/log/upstart/modemmanager.log /var/log/upstart/modemmanager.log.1.gz /var/log/upstart/module-init-tools.log /var/log/upstart/module-init-tools.log.1.gz /var/log/upstart/procps-static-network-up.log /var/log/upstart/procps-static-network-up.log.1.gz /var/log/upstart/procps-virtual-filesystems.log /var/log/upstart/procps-virtual-filesystems.log.1.gz /var/log/upstart/rsyslog.log /var/log/upstart/rsyslog.log.1.gz /var/log/upstart/ureadahead.log /var/log/upstart/ureadahead.log.1.gz /var/spool/anacron/cron.daily /var/spool/anacron/cron.monthly /var/spool/anacron/cron.weekly /var/spool/cron/atjobs /var/spool/cron/atspool /var/spool/cron/crontabs /var/spool/cups

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• Copy to USB memory stick really slow?

  - by Eloff

  When I copy files to the USB device, it takes much longer than in windows (same usb device, same port) it's faster than USB 1.0 speeds (1MB/s) but much slower than USB 2.0 speeds (12MB/s). To copy 1.8GB takes me over 10 minutes (it should be < 3 min.) I have two identical SanDisk Cruzer 8GB sticks, and I have the same problem with both. I have a super talent 32GB USB SSD in the neighboring port and it works at expected speeds. The problem I seem to see in the GUI is that the progress bar goes to 90% almost instantly, completes to 100% a little slower and then hangs there for 10 minutes. Interrupting the copy at this point seems to result in corruption at the tail end of the file. If I wait for it to complete the copy is successful. Any ideas? dmesg output below: [64059.432309] usb 2-1.2: new high-speed USB device number 5 using ehci_hcd [64059.526419] scsi8 : usb-storage 2-1.2:1.0 [64060.529071] scsi 8:0:0:0: Direct-Access SanDisk Cruzer 1.14 PQ: 0 ANSI: 2 [64060.530834] sd 8:0:0:0: Attached scsi generic sg4 type 0 [64060.531925] sd 8:0:0:0: [sdd] 15633408 512-byte logical blocks: (8.00 GB/7.45 GiB) [64060.533419] sd 8:0:0:0: [sdd] Write Protect is off [64060.533428] sd 8:0:0:0: [sdd] Mode Sense: 03 00 00 00 [64060.534319] sd 8:0:0:0: [sdd] No Caching mode page present [64060.534327] sd 8:0:0:0: [sdd] Assuming drive cache: write through [64060.537988] sd 8:0:0:0: [sdd] No Caching mode page present [64060.537995] sd 8:0:0:0: [sdd] Assuming drive cache: write through [64060.541290] sdd: sdd1 [64060.544617] sd 8:0:0:0: [sdd] No Caching mode page present [64060.544619] sd 8:0:0:0: [sdd] Assuming drive cache: write through [64060.544621] sd 8:0:0:0: [sdd] Attached SCSI removable disk

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• Database checksum features - redundant? useful?

  - by Eloff

  Just about every mainstream DB has a feature to calculate checksums per page, per sector, or per record. Now for a DB that does full recover after any crash, like PostgreSQL, is a checksum even useful? There will be no data loss as long as the xlog is ok, no matter what kind of corruption happened to the data itself, as the redo log is replayed every committed transaction will be restored. So checksums are useless on restore. Doesn't the filesystem or disk keep checksums anyway to detect corruption? So unless the checksum is per record, all it does is tell you there is corruption - which the OS should be yelling at you the minute you try to read it - so useless in operation? I can't imagine how a checksum can be helpful in any sane database - but since they all use them - I'd say that's just failure of imagination on my part. So how is it useful?

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• Is there any difference between null and 0 when assigning to pointers in unsafe code?

  - by Eloff

  This may seem odd, but in C (size_t)(void*)0 == 0 is not guaranteed by the language spec. Compilers are allowed to use any value they want for null (although they almost always use 0.) In C#, you can assign null or (T*)0 to a pointer in unsafe code. Is there any difference? (long)(void*)0 == 0 (guaranteed or not? put another way: IntPtr.Zero.ToInt64() == 0) MSDN has this to say about IntPtr.Zero: "The value of this field is not equivalent to null." Well if you want to be compatible with C code, that makes a lot of sense - it'd be worthless for interop if it didn't convert to a C null pointer. But I want to know if IntPtr.Zero.ToInt64() == 0 which may be possible, even if internally IntPtr.Zero is some other value (the CLR may or may not convert null to 0 in the cast operation) Not a duplicate of this question

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• Understanding CLR 2.0 Memory Model

  - by Eloff

  Joe Duffy, gives 6 rules that describe the CLR 2.0+ memory model (it's actual implementation, not any ECMA standard) I'm writing down my attempt at figuring this out, mostly as a way of rubber ducking, but if I make a mistake in my logic, at least someone here will be able to catch it before it causes me grief. Rule 1: Data dependence among loads and stores is never violated. Rule 2: All stores have release semantics, i.e. no load or store may move after one. Rule 3: All volatile loads are acquire, i.e. no load or store may move before one. Rule 4: No loads and stores may ever cross a full-barrier (e.g. Thread.MemoryBarrier, lock acquire, Interlocked.Exchange, Interlocked.CompareExchange, etc.). Rule 5: Loads and stores to the heap may never be introduced. Rule 6: Loads and stores may only be deleted when coalescing adjacent loads and stores from/to the same location. I'm attempting to understand these rules. x = y y = 0 // Cannot move before the previous line according to Rule 1. x = y z = 0 // equates to this sequence of loads and stores before possible re-ordering load y store x load 0 store z Looking at this, it appears that the load 0 can be moved up to before load y, but the stores may not be re-ordered at all. Therefore, if a thread sees z == 0, then it also will see x == y. If y was volatile, then load 0 could not move before load y, otherwise it may. Volatile stores don't seem to have any special properties, no stores can be re-ordered with respect to each other (which is a very strong guarantee!) Full barriers are like a line in the sand which loads and stores can not be moved over. No idea what rule 5 means. I guess rule 6 means if you do: x = y x = z Then it is possible for the CLR to delete both the load to y and the first store to x. x = y z = y // equates to this sequence of loads and stores before possible re-ordering load y store x load y store z // could be re-ordered like this load y load y store x store z // rule 6 applied means this is possible? load y store x // but don't pop y from stack (or first duplicate item on top of stack) store z What if y was volatile? I don't see anything in the rules that prohibits the above optimization from being carried out. This does not violate double-checked locking, because the lock() between the two identical conditions prevents the loads from being moved into adjacent positions, and according to rule 6, that's the only time they can be eliminated. So I think I understand all but rule 5, here. Anyone want to enlighten me (or correct me or add something to any of the above?)

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• Is it safe to catch an access violation in this scenario?

  - by Eloff

  I've read a lot, including here on SO that suggests this is a very bad idea in general and that the only thing you can do safely is exit the program. I'm not sure that this is true. This is for a pooling memory allocator that hands off large allocations to malloc. During pool_free() a pointer needs to be checked it it belongs to a pool or was allocated with malloc. By rounding the address down to the nearest 1MB boundary, I get a pointer to the beginning of a block of memory in the pool, or undefined if malloc was used. In the first case I can easily verify that the block of memory belongs to the pool, but, if it does not I will either fail this verification, or I will get an access violation (note that this is a read-only process). Could I not catch this with SEH (Windows) or handle the signal (POSIX) and simply treat it as a failed verification? (i.e. this is only possible if malloc was used, so pass the ptr to free())

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• POSIX: allocate 64KB on 64KB boundary.

  - by Eloff

  I would really like to actually only allocate 64KB of memory, not 128KB and then do the alignment manually - far too wasteful. VirtualAlloc on windows gives precisely this behavior. Supposedly there's code in SquirrelFish for doing this on just about every platform, but I haven't managed to locate it. Is there a space efficient way to allocate 64KB on a 64KB boundary in POSIX? Failing that, in Linux?

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• To OpenID or not to OpenID? Is it worth it?

  - by Eloff

  Does OpenID improve the user experience? Edit Not to detract from the other comments, but I got one really good reply below that outlined 3 advantages of OpenID in a rational bottom line kind of way. I've also heard some whisperings in other comments that you can get access to some details on the user through OpenID (name? email? what?) and that using that it might even be able to simplify the registration process by not needing to gather as much information. Things that definitely need to be gathered in a checkout process: Full name Email (I'm pretty sure I'll have to ask for these myself) Billing address Shipping address Credit card info There may be a few other things that are interesting from a marketing point of view, but I wouldn't ask the user to manually enter anything not absolutely required during the checkout process. So what's possible in this regard? /Edit (You may have noticed stackoverflow uses OpenID) It seems to me it is easier and faster for the user to simply enter a username and password in a signup form they have to go through anyway. I mean you don't avoid entering a username and password either with OpenID. But you avoid the confusion of choosing a OpenID provider, and the trip out to and back from and external site. With Microsoft making Live ID an OpenID provider (More Info), bringing on several hundred million additional accounts to those provided by Google, Yahoo, and others, this question is more important than ever. I have to require new customers to sign up during the checkout process, and it is absolutely critical that the experience be as easy and smooth as possible, every little bit harder it becomes translates into lost sales. No geek factor outweighs cold hard cash at the end of the day :) OpenID seems like a nice idea, but the implementation is of questionable value. What are the advantages of OpenID and is it really worth it in my scenario described above?

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• Can .NET AppDomains do this?

  - by Eloff

  I've spent hours reading up about AppDomains, but I'm not sure they work quite like I'm hoping. If I have two classes, Foo in AppDomain #1, Bar in AppDomain #2: App Domain #1 is the application. App Domain #2 is something like a plugin, and can be loaded and unloaded dynamically. AppDomain #2 wants to create Foo and use it. Foo uses lots of classes in AppDomain #1 internally. I don't want AppDomain #2 using object foo with reflection, I want it to use Foo foo, with all the static typing and compiled speed that goes with it. Can this be done considering that AppDomain #1, containing Foo, is never unloaded? If so, does any remoting take place here when using Foo? When I unload AppDomain #2, the type Foo is destroyed?

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• Any way to reserve but not commit memory in linux?

  - by Eloff

  Windows has VirtualAlloc, which allows you to reserve a contiguous region of address space, but not actually use any physical memory. Later when you want to use it (or part of it) you call VirtualAlloc again to commit the region of previously reserved pages. This is actually really useful, but I want to eventually port my application to linux - so I don't want to use it if I can't port it later. Does linux have a way to do this?

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