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  • Can I prevent a Linux user space pthread yielding in critical code?

    - by KermitG
    I am working on an user space app for an embedded Linux project using the 2.6.24.3 kernel. My app passes data between two file nodes by creating 2 pthreads that each sleep until a asynchronous IO operation completes at which point it wakes and runs a completion handler. The completion handlers need to keep track of how many transfers are pending and maintain a handful of linked lists that one thread will add to and the other will remove. // sleep here until events arrive or time out expires for(;;) { no_of_events = io_getevents(ctx, 1, num_events, events, &timeout); // Process each aio event that has completed or thrown an error for (i=0; i<no_of_events; i++) { // Get pointer to completion handler io_complete = (io_callback_t) events[i].data; // Get pointer to data object iocb = (struct iocb *) events[i].obj; // Call completion handler and pass it the data object io_complete(ctx, iocb, events[i].res, events[i].res2); } } My question is this... Is there a simple way I can prevent the currently active thread from yielding whilst it runs the completion handler rather than going down the mutex/spin lock route? Or failing that can Linux be configured to prevent yielding a pthread when a mutex/spin lock is held?

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  • My Red Gate Experience

    - by Colin Rothwell
    I’m Colin, and I’ve been an intern working with Mike in publishing on Simple-Talk and SQLServerCentral for the past ten weeks. I’ve mostly been working “behind the scenes”, making improvements to the spam filtering, along with various other small tweaks. When I arrived at Red Gate, one of the first things Mike asked me was what I wanted to get out of the internship. It wasn’t a question I’d given a great deal of thought to, but my immediate response was the same as almost anybody: to support my growing family. Well, ok, not quite that, but money was certainly a motivator, along with simply making sure that I didn’t get bored over the summer. Three months is a long time to fill, and many of my friends end up getting bored, or worse, knitting obsessively. With the arrogance which seems fairly common among Cambridge people, I wasn’t expecting to really learn much here! In my mind, the part of the year where I am at Uni is the part where I learn things, whilst Red Gate would be an opportunity to apply what I’d learnt. Thankfully, the opposite is true: I’ve learnt a lot during my time here, and there has been a definite positive impact on the way I write code. The first thing I’ve really learnt is that test-driven development is, in general, a sensible way of working. Before coming, I didn’t really get it: how could you test something you hadn’t yet written? It didn’t make sense! My problem was seeing a test as having to test all the behaviour of a given function. Writing tests which test the bare minimum possible and building them up is a really good way of crystallising the direction the code needs to grow in, and ensures you never attempt to write too much code at time. One really good experience of this was early on in my internship when Mike and I were working on the query used to list active authors: I’d written something which I thought would do the trick, but by starting again using TDD we grew something which revealed that there were several subtle mistakes in the query I’d written. I’ve also been awakened to the value of pair programming. Whilst I could sort of see the point before coming, I also thought that it was impossible that two people would ever get more done at the same computer than if they were working separately. I still think that this is true for projects with pieces that developers can easily work on independently, and with developers who both know the codebase, but I’ve found that pair programming can be really good for learning a code base, and for building up small projects to the point where you can start working on separate components, as well as solving particularly difficult problems. Later on in my internship, for my down tools week project, I was working on adding Python support to Glimpse. Another intern and I we pair programmed the entire project, using ping pong pair programming as much as possible. One bonus that this brought which I wasn’t expecting was that I found myself less prone to distraction: with someone else peering over my shoulder, I didn’t have the ever-present temptation to open gmail, or facebook, or yammer, or twitter, or hacker news, or reddit, and so on, and so forth. I’m quite proud of this project: I think it’s some of the best code I’ve written. I’ve also been really won over to the value of descriptive variables names. In my pre-Red Gate life, as a lone-ranger style cowboy programmer, I’d developed a tendency towards laziness in variable names, sometimes abbreviating or, worse, using acronyms. I’ve swiftly realised that this is a bad idea when working with a team: saving a few key strokes is inevitably not worth it when it comes to reading code again in the future. Longer names also mean you can do away with a majority of comments. I appreciate that if you’ve come up with an O(n*log n) algorithm for something which seemed O(n^2), you probably want to explain how it works, but explaining what a variable name means is a big no no: it’s so very easy to change the behaviour of the code, whilst forgetting about the comments. Whilst at Red Gate, I took the opportunity to attend a code retreat, which really helped me to solidify all the things I’d learnt. To be completely free of any existing code base really lets you focus on best practises and think about how you write code. If you get a chance to go on a similar event, I’d highly recommend it! Cycling to Red Gate, I’ve also become much better at fitting inner tubes: if you’re struggling to get the tube out, or re-fit the tire, letting a bit of air out usually helps. I’ve also become quite a bit better at foosball and will miss having a foosball table! I’d like to finish off by saying thank you to everyone at Red Gate for having me. I’ve really enjoyed working with, and learning from, the team that brings you this web site. If you meet any of them, buy them a drink!

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  • Heartbeat (Linux HA) and NetApp?

    - by Drew
    Does anyone have any experience setting up a high availability two node Linux cluster using heartbeat (linux-ha.org) and NetApp storage (preferably using SnapDrive for Linux)? Basically I would like to mount the same NetApp LUN over Fibre Channel to two servers in an Active/Passive mode (only one server can access the LUN at a time) Thanks!

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  • FFMPEG Install on EC2 - Amazon Linux

    - by Oliver Holmberg
    Hello Serverfault friends, I am about two days into attempting to install FFMPEG with dependencies on an AWS EC2 instance running the Amazon Linux AMI. I've installed FFMPEG on Ubuntu and Fedora systems with no problems in the past, and have read reportedly successful instructions on installing on Red Hat/Fedora. I have followed a number of tutorials and forum articles to do so, but have had no luck yet. As far as I can tell, the main problems are as followed: The amazon linux (Most similar to red-hat/centos) yum repositories don't have ffmpeg available. I have found instructions to update the repositories to include the required packages, but adding these repositories cause yum to fail in updating packages. (Also, I've read some cautionary tales about adding redhat/centos repositories to amazon linux that lead me to believe it may be a bad idea) (https://forums.aws.amazon.com/thread.jspa?messageID=229166) I have tried a more complicated method of downloading the source tarball, compiling, and installing, but this always fails due to missing dependencies and other errors. On to my question: Has anyone successfully installed FFMPEG on Amazon Linux? Is there a fundamental incompatibility? If anyone could share specific instructions on installing ffmpeg on amazon linux I would be greatly appreciative. Any other insights/experiences would also be appreciated. Thanks in advance, Oliver

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  • backupexec 12.5 not following symlinks on linux agent

    - by Peter Carrero
    Ok, we are at a loss here trying to backup a linux box to a backupexec server... we got a backupexec 12.5 server and a "backupexec for windows servers linux agent" (sigh) running on one of our linux boxes. When a backup runs, we get exceptions reported for our symbolic links. it says something like: BACKUP- \\<servername>\[ROOT] File \\<servername>\[ROOT]/<foldername>/<symlink> is in the backup selection list but was not found. Looking at the selection list, the symlink shows as a 1k file on BUE. Tools-Options-Backup has Backup files and directories by following symbolic links/junction points selected. These same checkboxes are selected on the Job Setup-Job Properties-Edit Template-Advanced Additionally, all the checkboxes are checkeced on Tools-Options-Linux, Unix, and Macintosh and on the Job Set-Job Properties-Edit Template-Linux, Unix, and Macintosh. These checkboxes read: "Preserve change time", "Follow local mount points", "Follow remote mount points", "Backup contents of soft-linked directories" and "Lock remote files", but apparently changing those options produce the same result. Any help on how to get BUE to make a proper backup would be greatly appreciated. Thanks.

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  • Best book for learning linux shell scripting?

    - by chakrit
    I normally works on Windows machines but on some occasions I do switch to development on linux. And my most recent project will be written entirely on a certain linix platforms (not the standard Apache/MySQL/PHP setup). So I thought it would pay to learn to write some linux automation script now. I can get around the system, start/stop services, compile/install stuffs fine. Those are probably basic drills for a programmer. But if, for example, I wanted to deploy a certain application automatically to a newly minted linux machine every month I'd love to know how to do it. So if I wanted to learn serious linux shell scripting, what book should I be reading? Thanks

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  • Linux installation analysis

    - by blunders
    "Ending company IT Admin relationship" has a good checklist for taking over an existing IT system, but I'm wondering as it relates to Linux: What is the most effective way to assess the scope of existing custom configurations, installs, scripts, etc done? Is there any software that will check if the kernel, system files, etc mirror the default files for the version installed? At this point I don't know what distro of Linux the server (though using Netcraft I do know the server appears to be Linux) -- so it's possible without knowing that information that this would be a hard question to answer.

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  • Windows CA to issue certificate to authenticate SSH to a Linux server

    - by BArnold
    I have a Windows Server Root Certificate Authority, Linux SSH server, and users with Windows SSH clients. The Linux box is not part of the AD domain (and probably never will be [sigh]) OpenSSH 5.4 and above supports X.509 certiicate based authentication. I am trying to find a way to use my Windows Certificate Authority to issue certificates for authentication of the users when the SSH to the Linux box. I do not want to have to generate a keypair on each user's desktop. And we want the certificates controlled and revokable at the Windows CA. My question is not exactly the same as SSH from Windows to Linux with AD certificates (and the referenced moelinux.net seems to be down) I have searched Google a lot, and haven't found much results about how to accomplish this. An answer doesn't necessarily have to include a full tutorial, even some hints about what to search on or pointers to some references may be helpful.

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  • How does the EFI partition work and can I boot an x86 OS with a bootx64.efi file?

    - by Ian
    I have a Thinkpad X230 laptop and I want to install Linux Mint Debian Edition along side Windows 7 on my GPT formatted SSD with the BIOS in UEFI mode. The problem is that I don't understand how EFI booting works. There seems to be an EFI partition involved with some folders and binary files in it. GRUB 2 seems to be able to make more folders in it (I followed this guide http://www.thinkwiki.org/wiki/UEFI_Firmware), but it appears that the only file that does anything is the bootx64.efi file in the /efi/boot folder of the EFI partition (I am not sure if this is always the case, but it appears to be the case for my laptop http://www.thinkwiki.org/wiki/Category:X220). Here is what I have been able to do: I can install Linux Mint Debian Edition x86 with the BIOS in BIOS mode on my SSD. I can then install grub-efi and follow the guide linked above. The problem is that I don't get a GRUB prompt when I switch the BIOS to UEFI mode. It just boots Windows. It appears that I can either boot from the SSD or something called "Windows Boot Manager". If I replace the bootx64.efi with the file created by GRUB, I can no longer boot directly from the SSD. Booting from "Windows Boot Manager" still works fine. I realize that the guide says to use x64 Linux, but Linux Mint Debian Edition x64 hangs during the install process. I am really confused. What should I do? Can anyone explain how the EFI boot partition works? Can a bootx64.efi boot an x86 OS? Should I just give up with using UEFI? I haven't been able to find very much useful information about using Debian based operating systems with UEFI. Thanks, Ian

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  • Gre Tunnel Cisco Linux traffic forwarding

    - by mezgani
    I setup a gre tunnel a cisco router and a Linux machine, the tunnel interface in the Linux box named pic. Well i have to forward traffic coming from cisco through the Linux box. the rules i've set in the Linux box is described as follow: echo "1" /proc/sys/net/ipv4/ip_forward iptables -A INPUT -p 47 -j ACCEPT iptables -A FORWARD -i ppp0 -j ACCEPT iptables -A FORWARD -i pic -o ppp0 -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -A FORWARD -i ppp0 -o pic -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE I see the traffic coming from tunnel and forwarded to internet but no reply from sent packet. May i miss something like a routing rule.

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  • Setting up Samba shares on a Linux VPS

    - by 101265052760541259879
    Hi, I'm trying to set up a folder that can be accessed via Windows clients over the net on my Linux VPS on which our companies website resides. I know a little bit about Linux, and have used Samba before to browse Windows shares from a Linux laptop. I'm guessing it's possible to do the reverse - to share a folder from Linux TO a Windows client. I have root SSH access to the VPS, would anyknow know what steps I need to take to set up the share, and how I can secure it, ideally with a simple username/password so the Windows clients can connect easily? Many thanks, Jack

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  • SQL Server on Linux

    - by TimothyAWiseman
    For a particular project that is coming up, I am trying to expand my knowledge of Linux, so I am going to set up a Linux system at home. Rather than dual booting, I am thinking about putting SQL Server on a Windows Virtual Machine with Linux as the host at least until this project is over when I will probably switch back to Linux. So, I have a couple of different, but interrelated questions: How well does this work? This is only a test machine at home, so I can easily accept a fair bit of degradation, but if it is going to be a horrible reduction in performance I will dual boot instead. Is there a particular virtual machine manager I should look at to go this route? Since this is my personal machine, price is an issue but I am quite happy to pay a reasonable amount. And finally, given the choice of VMM, is there a particular Linux Distro I should be looking at? [This has been cross posted at Ask.SqlServerCentral.com . I think it may be appropriate at both sites. ]

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  • How do I recover from a Linux CentOS 4.6 Operating System Crash

    - by Greg Omebije
    Our x86 Linux server running CentOS4.6 has crashed. The machine boots only to the Grub prompt. We have tried using the "rescue mode" to recover the System, but it hasn't worked. How can we fix this problem, so that the machine boots normally? How can we fix this problem to the point were we can recover our files from the server Our Linux Server Configuration: Dell PowerEdge 1950 Intel Xeon 2 HDD (146GB each) 4GB RAM Hardware and Software raid setup CentOS 4.6 We used Sysrecord to boot the computer: the following are the output of fdisk -l Disk /dev/sda: 293.3 GB, 292326211584 255 heads, 63 sectors/track, 35539 Cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x00000080 Device Boot Start End Blocks Id System /dev/sda1 * 1 13 104391 83 Linux /dev/sda2 14 17769 142625070 8e Linux LVM

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  • Running Montavista Linux kernel 2.6.21 on XEN

    - by Josh
    I've been assigned the task of getting our MontaVista Linux (2.6.21 kernel) running on Xen. We'll be running Xen in -hvm- mode. My Xen version is 3.4.0 (linux kernel 2.6.18) and am unable to run MontaVista Linux (kernel 2.6.21) in hvm mode. Does anyone have suggestions?

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  • backupexec 12.5 not following symlinks on linux agent

    - by Peter Carrero
    Ok, we are at a loss here trying to backup a linux box to a backupexec server... we got a backupexec 12.5 server and a "backupexec for windows servers linux agent" (sigh) running on one of our linux boxes. When a backup runs, we get exceptions reported for our symbolic links. it says something like: BACKUP- \\<servername>\[ROOT] File \\<servername>\[ROOT]/<foldername>/<symlink> is in the backup selection list but was not found. Looking at the selection list, the symlink shows as a 1k file on BUE. Tools-Options-Backup has Backup files and directories by following symbolic links/junction points selected. These same checkboxes are selected on the Job Setup-Job Properties-Edit Template-Advanced Additionally, all the checkboxes are checkeced on Tools-Options-Linux, Unix, and Macintosh and on the Job Set-Job Properties-Edit Template-Linux, Unix, and Macintosh. These checkboxes read: "Preserve change time", "Follow local mount points", "Follow remote mount points", "Backup contents of soft-linked directories" and "Lock remote files", but apparently changing those options produce the same result. Any help on how to get BUE to make a proper backup would be greatly appreciated. Thanks.

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  • Dual booting Linux/Win7, Grub refuses to load Win7

    - by JohnB
    Decided to give Linux Mint a try (Ubuntu's interface annoys me), so I installed it with the intention of dual booting with Windows 7. Installation went fine, but now I can only boot into Linux Mint. Grub lists two Windows 7 menu options, but selecting either of them causes an "unknown file system" error and dumps me into a Grub recovery prompt. There, I have to manually reset the root and prefix options, as they reset hd0,msdos6 when they should be hd0,msdos5. I ran Boot Repair twice, once to fix grub errors, once to rebuild the MBR, but it didn't fix anything. Here is the log: http://paste.ubuntu.com/1029675/ fdisk output: Device Boot Start End Blocks Id System /dev/sda1 * 2048 206847 102400 7 HPFS/NTFS/exFAT /dev/sda2 206848 1486249145 743021149 7 HPFS/NTFS/exFAT /dev/sda3 1486249982 1953523711 233636865 5 Extended /dev/sda5 1486249984 1945141247 229445632 83 Linux /dev/sda6 1945143296 1953523711 4190208 82 Linux swap / Solaris grub.cfg: ### BEGIN /etc/grub.d/30_os-prober ### menuentry "Windows 7 (loader) (on /dev/sda1)" --class windows --class os { insmod part_msdos insmod ntfs set root='(hd0,msdos1)' search --no-floppy --fs-uuid --set=root 86184D18184D091F chainloader +1 } menuentry "Windows 7 (loader) (on /dev/sda2)" --class windows --class os { insmod part_msdos insmod ntfs set root='(hd0,msdos2)' search --no-floppy --fs-uuid --set=root 56D84F84D84F60FB chainloader +1 } ### END /etc/grub.d/30_os-prober ### I have found a few similar troubleshooting guides so far, but so far no amount of updating/configuring Grub has been successful. Last resort is, I suppose, use the W7 recovery disc and start over. Thanks in advance! Linux Mint 13 Maya, 64-bit Windows 7 Home Edition, 64-bit

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  • Linux Mint networking not enabled in VMWare

    - by Igor Ganapolsky
    Hi, I installed Linux Mint in VMware, and I do not understand how to enable networking. My VMware settings use a bridged connection. My other linux distros run fine in vmware - networking works for them. But Linux Mint is the only one that isn't obtaining an ip address. Furthermore, I do not see an option in the administrative menu of Mint to enable networking... Please help. Thanks, Igor

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  • "Learning" Linux

    - by Strider
    I've been interested in computers for a long time and have fiddled with a lot of stuff which includes Linux. I started out with Red Hat when I was young (around 13) and lost all data, converting a FAT32 drive to something else. Later it was Knoppix which was really helpful in recovery and such. Then, it was Ubuntu. Also, I fiddled with Arch for some time, but, it breaks too often for my liking (maybe, I should have been more careful). Anyway, currently I use Ubuntu 9.04. I want to dig deeper into the Linux world now. I want to learn how things work and use the terminal more. I am a programmer as well, so, it will help a lot. So, the thing I wanted to ask were: Good books to learn and understand Linux Good habits to use Linux more efficiently. Good tools about which I should know. Amount of time you set aside to learn about new things each day. As a programmer, how do you setup and use Linux efficiently. Long list. I will be grateful to the answerers.

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  • windows 7 vs linux on ssd

    - by wushugene
    Why did my old windows 7 install boot faster/run smoother & cooler than each the three linux distros I have recently tried (ubuntu 12.04 unity, linux mint 13 MATE, and fedora 17 on gnome 3.4)?. I have tweaked my linux installs for the ssd (enabling trim, disabling swap, etc.) I'm using an Acer TravelMate with i5-2410m processor, intel hd 3000 graphics, 8 gigs of ram, and a 256 gb samsung 830 ssd. Thanks!

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  • Linux group permissions getting overwritten by owner

    - by Andy
    I am not a user of Linux, but I am encountering some permissions problems with it that I hope someone can shed some light on. Bit of background: A colleague of mine has a Linux box (running Debian I believe) with an SVN repository on it. The repository directory and files 'owner' is my colleauge. We are both members of a group called 'users'. He manages several projects both Linux and Windows apps, while I have one Windows app. For the Windows apps, we both use TortoiseSVN via an SSH link to commit/update. Performing the command 'ls -l' shows the repository files and folders on the Linux box to have the following permissions: -rwxrwx--- john users However, when my colleauge commits to the repository, the permissions change to: -rwxrwx--- john john This then means I get 'Permission denied' when trying to access the repository myself as it appears that the group permissions have been overwritten with only 'owner' permissions. To fix this, a 'chown -R' command is applied to the files/folders to set the permissions back to owner/group, but each time he writes to the repository, the issue repeats. I'm not sure if this is solely an SVN problem, or a more fundamental owner/group issue. Anyone any clue on how to stop this happening, or where to go and look? I'm trying to help out my colleague who is having some trouble resolving this issue. Apologies for the vague info, I hope I have conveyed the problem clear enough. Like I say, I am not a Linux user, I have only put down what I have managed to pick up from looking over his shoulder. Thanks for any pointers I can pass on!

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  • I get a Segmentation fault when doing apt-get util-linux

    - by Adam
    I've found that a lot of upgrade commands and Apache on my system are failing with Segmentation faults. I don't know if this is the main one, but a lot of packages depend on util-linux: root@myUbuntuHardyHeronServer:~# apt-get install util-linux Reading package lists... Done Building dependency tree Reading state information... Done The following packages will be upgraded: util-linux 1 upgraded, 0 newly installed, 0 to remove and 72 not upgraded. 20 not fully installed or removed. Need to get 0B/441kB of archives. After this operation, 0B of additional disk space will be used. (Reading database ... 20547 files and directories currently installed.) Preparing to replace util-linux 2.13.1-5ubuntu2 (using .../util-linux_2.13.1-5ub untu3.1_i386.deb) ... Unpacking replacement util-linux ... Segmentation fault dpkg: warning - old post-removal script returned error exit status 139 dpkg - trying script from the new package instead ... Segmentation fault dpkg: error processing /var/cache/apt/archives/util-linux_2.13.1-5ubuntu3.1_i386 .deb (--unpack): subprocess new post-removal script returned error exit status 139 Segmentation fault dpkg: error while cleaning up: subprocess post-removal script returned error exit status 139 Errors were encountered while processing: /var/cache/apt/archives/util-linux_2.13.1-5ubuntu3.1_i386.deb E: Sub-process /usr/bin/dpkg returned an error code (1)

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  • How to unsquash and mount arch linux live CD

    - by steffen
    I am following this manual to install Arch Linux from within another Linux distro with the help of an Arch Linux live CD. Here is what I did: sudo mount -o loop Downloads/archlinux-2012.11.01-dual.iso arch_iso/ unsquashfs -d squashfs-root/ arch_iso/arch/x86_64/root-image.fs.sfs This results in a directory squashfs-root/ containing one file: root-image.fs I assume that this is not what I want. I want to see something that looks like a Linux root folder. If I follow these steps: "mount the file system" with mount -B /squashfs-root ${livecd_arch} and mount -t proc /proc ${livecd_arch}/proc, I get error messages like: mount: mount point /home/me/arch_root//proc does not exist What am I missing? Thanks!

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