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  • Problem with .release behavior in file_operations

    - by Yannick
    Hello, I'm dealing with a problem in a kernel module that get data from userspace using a /proc entry. I set open/write/release entries for my own defined /proc entry, and manage well to use it to get data from userspace. I handle errors in open/write functions well, and they are visible to user as open/fopen or write/fwrite/fprintf errors. But some of the errors can only be checked at close (because it's the time all the data is available). In these cases I return something different than 0, which I supposed to be in some way the value 'close' or 'fclose' will return to user. But whatever the value I return my close behave like if all is fine. To be sure I replaced all the release() code by a simple 'return(-1);' and wrote a program that open/write/close the /proc entry, and prints the close return value (and the errno). It always return '0' whatever the value I give. Behavior is the same with 'fclose', or by using shell mechanism (echo "..." /proc/my/entry). Any clue about this strange behavior that is not the one claimed in many tutorials I found? BTW I'm using RHEL5 kernel (2.6.18, redhat modified), on a 64bit system. Thanks. Regards, Yannick

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  • OSS4 on Debian Squeeze

    - by mit
    Hi, I am trying to get OSS4 to work on a Debian Squeeze 64 bit machine with an usb sound adapter. There is no sound from this adapter at the present, although it worked just before on the previous installation. You can see the output of some commands here: $ sudo /etc/init.d/oss4-base restart Stopping Open Sound System: SNDCTL_MIX_EXTINFO: No such device or address done. Starting Open Sound System: done (OSS is already loaded). $ sudo /etc/init.d/oss4-base stop Stopping Open Sound System: SNDCTL_MIX_EXTINFO: No such device or address done. $ sudo /etc/init.d/oss4-base start Starting Open Sound System: done (OSS is already loaded). $ ossinfo Version info: OSS 4.2 (b 2002/201001250441) (0x00040100) GPL Platform: Linux/x86_64 2.6.32-5-xen-amd64 #1 SMP Fri Dec 10 17:41:50 UTC 2010 (pc11) Number of audio devices: 2 Number of audio engines: 2 Number of MIDI devices: 0 Number of mixer devices: 2 Device objects 0: osscore0 OSS core services 1: oss_hdaudio0 ATI HD Audio interrupts=0 (613) HD Audio controller ATI HD Audio Vendor ID 0x10024383 Subvendor ID 0x10192816 Codec 0: Not present 2: oss_usb0 USB audio core services 3: usb0d8c0126-0 USB sound device 4: usb0d8c0126-1 USB sound device 5: usb0d8c0126-2 USB sound device 6: usb0d8c0126-3 USB sound device MIDI devices (/dev/midi*) Mixer devices 0: (USB sound device )(Mixer 0 of device object 3) 1: USB sound device (Mixer 0 of device object 5) Audio devices (USB sound device play /dev/oss/usb0d8c0126-1/pcm0 ) (device index 0) USB sound device play /dev/oss/usb0d8c0126-3/pcm0 (device index 1) Nodes /dev/dsp -> /dev/oss/usb0d8c0126-1/pcm0 /dev/dsp_out -> /dev/oss/usb0d8c0126-1/pcm0 /dev/dsp_mmap -> /dev/oss/usb0d8c0126-1/pcm0 $ osstest Sound subsystem and version: OSS 4.2 (b 2002/201001250441) (0x00040100) Platform: Linux/x86_64 2.6.32-5-xen-amd64 #1 SMP Fri Dec 10 17:41:50 UTC 2010 *** Scanning sound adapter #-1 *** /dev/oss/usb0d8c0126-1/pcm0 (audio engine 0): USB sound device play - Device not present - Skipping *** Scanning sound adapter #-1 *** /dev/oss/usb0d8c0126-3/pcm0 (audio engine 1): USB sound device play - Performing audio playback test... /dev/oss/usb0d8c0126-3/pcm0: No such file or directory Can't open the device *** Some errors were detected during the tests *** $ ossxmix /dev/oss/usb0d8c0126-2/mix0: No such file or directory No mixers could be opened $ ossmix SNDCTL_MIX_EXTINFO: No such device or address ad@pc11:~$ man ossmix ad@pc11:~$ ossmix -a SNDCTL_MIX_EXTINFO: No such device or address ad@pc11:~$ man ossmix ad@pc11:~$ ossmix -D SNDCTL_MIX_EXTINFO: No such device or address ad@pc11:~$ ossmix -D 0 SNDCTL_MIX_EXTINFO: No such device or address ad@pc11:~$ man ossmix ad@pc11:~$ ossxmix /dev/oss/usb0d8c0126-2/mix0: No such file or directory No mixers could be opened How can I make oss sound work? I can add more information if necessary.

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  • Linux equivalent to Mac OS X's fs_usage

    - by Khai
    Is there a Linux equivalent to the Mac OS X command fs_usage? According to the man page it does the following: "report system calls and page faults related to filesystem activity in real-time". I suppose one option would be to use strace and filter the data, however the fs_usage command allows all the processes running on the system to be "traced" at the same time. Here's an example output: 03:44:25 stat64 erences/ByHost/org.mozilla.firefox.69AC0B48-F675-5045-B873-A28B119C33E7.plist 0.000029 firefox 03:44:25 stat64 /Users/**********/Library/Preferences 0.000011 firefox 03:44:25 statfs64 /Users/**********/Library/Preferences 0.000004 firefox 03:44:25 open /Users/**********/Library/Preferences/org.mozilla.firefox.plist.lockfile 0.000090 firefox 03:44:25 stat64 /Users/**********/Library/Preferences/org.mozilla.firefox.plist 0.000004 firefox 03:44:25 stat64 /Users/**********/Library/Preferences 0.000002 firefox 03:44:25 open /Users/**********/Library/Preferences/org.mozilla.firefox.plist.vjLkANe 0.000100 firefox Any ideas?

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  • SCSI direct-access device appears as multiple lun's

    - by unixdj
    I have a similarly described problem to this question: http://superuser.com/questions/90181/same-scsi-drive-appears-multiple-times-on-the-controller-list where a SCSI direct-access device appears as multiple lun's, when it should only be one. The device is a SCSI-1 device, the SCSI controller card is an Adaptec AHA-7850 (rev 03), and system is PC / Linux 2.6. This device worked fine with RHEL4, and appeared as a single device / lun when the OS booted, but I've just tried plugging the device into a newer Linux disto (CentOS 5.4) and it now sees the device as 8 luns; with consequently 8 device files /dev/sgb to /dev/sgi. Any clues of how to figure out where the problem / fix is, would be great.

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  • Advantages of Ubuntu LTS versions over regular Ubuntu?

    - by Adam Matan
    Do the LTS versions of Ubuntu have any advantages for the non-paying customers (who don't get any support?) From the tech spec only, these versions seem outdated in many aspects - mainly drivers and installed software versions. For instance, My previous (bounty!) problem regarding the AGN 5100 drivers would have been solved under Ubuntu 9.04.

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  • Linux memory fragmentation

    - by Raghu
    Hi all, Is there a way to detect memory fragmentation on linux ? This is because on some long running servers I have noticed performance degradation and only after I restart process I see better performance. I noticed it more when using linux huge page support -- are huge pages in linux more prone to fragmentation ? I have looked at /proc/buddyinfo in particular. I want to know whether there are any better ways(not just CLI commands per se, any program or theoretical background would do) to look at it.

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  • Loading the 'pktgen' module on Ubuntu Server

    - by StackedCrooked
    I would like to enable and use the pktgen module on Ubuntu Server. I have enabed the module by adding a line containing 'pktgen' to the /etc/modules file. After rebooting it seems that the module is successfully loaded because the directory /proc/net/pktgen exists. However when trying to run the first sample I get these errors: root@ubuntu:~# bash ./pktgen.conf-1-1 Removing all devices Adding eth4 Setting max_before_softirq 10000 Configuring /proc/net/pktgen/eth4 ./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory ./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory ./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory ./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory ./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory ./pktgen.conf-1-1: line 9: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory cat: /proc/net/pktgen/eth4: No such file or directory Running... ctrl^C to stop Done It turns out the script simply unable to write a file to the /proc/net/pktgen directory. When I try this manually it fails as well: root@ubuntu:~# cd /proc/net/pktgen/ root@ubuntu:/proc/net/pktgen# touch eth4 touch: cannot touch `eth4': No such file or directory Can anyone help me make it work? I'm using Ubuntu version: 2.6.32-21-server. Fixed I apologize for keeping this post not up to date. I was able to fix it. If I remember well the cause of the error was that eth4 did not exist, or did not have the 'online' status. Anyway, it is fixed now.

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  • FreeBSD Listen Queue Overflows - can't increase max queue size

    - by Harry
    I have a decently high trafficked FreeBSD Nginx server, and I'm starting to get a large number of listen queue overflows: [root@svr ~]# netstat -sp tcp | fgrep listen 80361931 listen queue overflows [root@svr ~]# netstat -Lan | grep "*.80" tcp4 192/0/128 *.80 [root@svr ~]# sysctl kern.ipc.somaxconn kern.ipc.somaxconn: 12288 [root@svr ~]# However I can't seem to increase the max listen queue length past 128. I've increased kern.ipc.somaxconn, but it's not changing the max. Am I missing something? Thanks!

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  • Linux Mint 14 severe overheating

    - by agvares
    I've tried switching to Mint (it was Mint 12) about 6 months ago, but failed to do it due to enormous overheating which made it virtually impossible to run any applications more complex than Gedit. Time had passed, and now I'm back again with Mint 14, but feeling way more determined. What I face are the following issues: 1) Great overheating (and by great I mean that just by doing nothing my CPU temp is floating around 70-75 C, which I find a lot) 2) Running multiple applications (let's say Chrome, Skype and Pidgin) results in critical overheating and immediate shutdown of the system 3) Due to the stuff listed above, my battery drains in about 10-15 minutes, pretty much turning my laptop into a crippled desktop machine I've got a HP-dv6 laptop (i7, 6gb RAM, dual graphics) Here's the output of lspci: 00:00.0 Host bridge: Intel Corporation 2nd Generation Core Processor Family DRAM Controller (rev 09) 00:01.0 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09) 00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09) 00:16.0 Communication controller: Intel Corporation 6 Series/C200 Series Chipset Family MEI Controller #1 (rev 04) 00:1a.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #2 (rev 05) 00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 05) 00:1c.0 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 1 (rev b5) 00:1c.1 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 2 (rev b5) 00:1c.2 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 3 (rev b5) 00:1c.3 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 4 (rev b5) 00:1d.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #1 (rev 05) 00:1f.0 ISA bridge: Intel Corporation HM65 Express Chipset Family LPC Controller (rev 05) 00:1f.2 SATA controller: Intel Corporation 6 Series/C200 Series Chipset Family 6 port SATA AHCI Controller (rev 05) 00:1f.3 SMBus: Intel Corporation 6 Series/C200 Series Chipset Family SMBus Controller (rev 05) 01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Whistler XT [AMD Radeon HD 6700M Series] 07:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 06) 0d:00.0 Network controller: Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller (rev 01) 13:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS5209 PCI Express Card Reader (rev 01) 19:00.0 USB controller: NEC Corporation uPD720200 USB 3.0 Host Controller (rev 04) what i've tried to do already: 1) I've edited my grub file to add some "splash" arguments there 2) Installed jupiter and powertop 3) Tried to upgrade to newer kernels (up to 3.8), btw running anything newer than 3.5 results in both resolution and wi-fi detection fail 4) Read lots of forum threads devoted to the topic So, my question is simple: What else might I do to become finally able to use Mint as my default OS without the risk of being burned alive by the CPU heat?

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  • Implication of variable context switching time

    - by Rob
    Hi, I know that constant switching time of the Linux scheduler was a big achievement. I was just asking myself the question what would be the implication of a non-constant switching time. The only obvious reason I can think of is real-time systems where we have to meet deadlines. There it is obviously no ideal if the switching time is "random". Are there any other good reasons that favour constant switching times? Many thanks, Rob

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  • please explain my fio results - is O_SYNC|O_DIRECT misbehaving on linux?

    - by Zoltan
    I'm going mad over figuring out what the problem could be with one of our storage boxes. With a simple fio script I'm testing random writes using bs=1M and direct=1. The SSD is a Samsung 840pro attached to an LSI HBA (3Gbit/s ports). This is the result I'm getting under FreeBSD 9.1: WRITE: io=13169MB, aggrb=224743KB/s, minb=224743KB/s, maxb=224743KB/s, mint=60002msec, maxt=60002msec This is regardless of sync being set to 0 or 1. On linux, this is the result with sync=0: WRITE: io=14828MB, aggrb=253060KB/s, minb=253060KB/s, maxb=253060KB/s, mint=60001msec, maxt=60001msec and with sync=1: WRITE: io=6360.0MB, aggrb=108542KB/s, minb=108542KB/s, maxb=108542KB/s, mint=60001msec, maxt=60001msec My understanding is that since I'm operating on the raw block device, O_SYNC should not make any difference - there's no filesystem, any barrier, anything between the writes and the drive itself. Especially with O_DIRECT|O_SYNC set. Any ideas? For reference, here's the fio script I'm testing with: [global] bs=1M ioengine=sync iodepth=4 size=16g direct=1 runtime=60 filename=/dev/sdh sync=1 [rand-write] rw=randwrite stonewall

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  • How to stop a infinite running process(ztail) started by a ssh session after that session is closed

    - by Sanath Adiga
    I have a peculiar problem. My server supports multiple ssh session simultaneously, so that multiple admins can manage it simultaneously. We have a command which calls ztail to show the compressed log files and when the current ssh session is closed (without pressing ctrlc, to stop the tail command), the command should ideally stop working. But what I observed when I start a new ssh session is that the process ztail is still running in the background and consuming CPU, even though the previous session was closed. How can I determine when the session is closed, so that I can use that variable/flag to close/stop any commands initiated by that previously closed session?

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  • Maximum number of files in one ext3 directory while still getting acceptable performance?

    - by knorv
    I have an application writing to an ext3 directory which over time has grown to roughly three million files. Needless to say, reading the file listing of this directory is unbearably slow. I don't blame ext3. The proper solution would have been to let the application code write to sub-directories such as ./a/b/c/abc.ext rather than using only ./abc.ext. I'm changing to such a sub-directory structure and my question is simply: roughly how many files should I expect to store in one ext3 directory while still getting acceptable performance? What's your experience? Or in other words; assuming that I need to store three million files in the structure, how many levels deep should the ./a/b/c/abc.ext structure be? Obviously this is a question that cannot be answered exactly, but I'm looking for a ball park estimate.

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  • Find out which task is generating a lot of context switches on linux

    - by Gaks
    According to vmstat, my Linux server (2xCore2 Duo 2.5 GHz) is constantly doing around 20k context switches per second. # vmstat 3 procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 2 0 7292 249472 82340 2291972 0 0 0 0 0 0 7 13 79 0 0 0 7292 251808 82344 2291968 0 0 0 184 24 20090 1 1 99 0 0 0 7292 251876 82344 2291968 0 0 0 83 17 20157 1 0 99 0 0 0 7292 251876 82344 2291968 0 0 0 73 12 20116 1 0 99 0 ... but uptime shows small load: load average: 0.01, 0.02, 0.01 and top doesn't show any process with high %CPU usage. How do I find out what exactly is generating those context switches? Which process/thread? I tried to analyze pidstat output: # pidstat -w 10 1 12:39:13 PID cswch/s nvcswch/s Command 12:39:23 1 0.20 0.00 init 12:39:23 4 0.20 0.00 ksoftirqd/0 12:39:23 7 1.60 0.00 events/0 12:39:23 8 1.50 0.00 events/1 12:39:23 89 0.50 0.00 kblockd/0 12:39:23 90 0.30 0.00 kblockd/1 12:39:23 995 0.40 0.00 kirqd 12:39:23 997 0.60 0.00 kjournald 12:39:23 1146 0.20 0.00 svscan 12:39:23 2162 5.00 0.00 kjournald 12:39:23 2526 0.20 2.00 postgres 12:39:23 2530 1.00 0.30 postgres 12:39:23 2534 5.00 3.20 postgres 12:39:23 2536 1.40 1.70 postgres 12:39:23 12061 10.59 0.90 postgres 12:39:23 14442 1.50 2.20 postgres 12:39:23 15416 0.20 0.00 monitor 12:39:23 17289 0.10 0.00 syslogd 12:39:23 21776 0.40 0.30 postgres 12:39:23 23638 0.10 0.00 screen 12:39:23 25153 1.00 0.00 sshd 12:39:23 25185 86.61 0.00 daemon1 12:39:23 25190 12.19 35.86 postgres 12:39:23 25295 2.00 0.00 screen 12:39:23 25743 9.99 0.00 daemon2 12:39:23 25747 1.10 3.00 postgres 12:39:23 26968 5.09 0.80 postgres 12:39:23 26969 5.00 0.00 postgres 12:39:23 26970 1.10 0.20 postgres 12:39:23 26971 17.98 1.80 postgres 12:39:23 27607 0.90 0.40 postgres 12:39:23 29338 4.30 0.00 screen 12:39:23 31247 4.10 23.58 postgres 12:39:23 31249 82.92 34.77 postgres 12:39:23 31484 0.20 0.00 pdflush 12:39:23 32097 0.10 0.00 pidstat Looks like some postgresql tasks are doing 10 context swiches per second, but it doesn't all sum up to 20k anyway. Any idea how to dig a little deeper for an answer?

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  • server will not reply (syn -ack)

    - by Brent
    I like to use the following commands to manage 'TIME_WAIT', in the hope to free up resources. echo 20 > /proc/sys/net/ipv4/tcp_fin_timeout sysctl -w net.ipv4.tcp_tw_reuse=1 sysctl -w net.ipv4.tcp_tw_recycle=1 I found something interesting while doing a tcpdump. Sometimes if a client makes a connection (syn), the server will not reply (syn -ack). My question is, could it be because of the top three commands.

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  • A tiered approach to cloning linux partitons

    - by Djurdjura
    I'm looking at a strategy for cloning Linux (root) partitions without having to use a Live CD. Literature suggests rightly that the source and target partitions must be umounted to be able to get a clean clone. This assumes that you need to use a LiveCD. I was wondering if instead of requiring a LiveCD, if using a 3rd partition that would emulate the LiveCD functionality, if we can't achieve the same functionality. In other words, at a high level a system with 3 partitions (all bootable): Rescue Partition (LiveCD emulation) Running Partition (Source) Backup Partition (Destination) All 3 partitions are LVMS. When it's time to clone the source partition to the backup (destination) partition, we would boot to the rescue partition, unmount the other 2 partitions (is it required?), run disk check on the source, copy to the destination (dd or simple copy to avoid replicating the defragmentation from the source), run disk check on the destination partition, update Grub menu list to force boot from either partition, and reboot into that partition. My question, is it an approach that you'd recommend? MBR in all this? Any gotchas or extra checks required? Thanks, D. PS. On recommendation from members, posting here instead of stackoverflow.com.

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  • linux/unix filesystem permissions hack/feature

    - by selden
    Can linux or other unix create a file that no user, including root, can modify unless they have the secret key? By "have the secret key" I mean they are using some crypto scheme. Here's a scenario if you aren't already downvoting: Bob encrypts something about file /foo (maybe inode?) using secret key K Alice tries "sudo rm /foo" and gets permission denied, so she decrypts something about file /foo using secret key K and then "sudo rm /foo" succeeds.

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  • snow leopard: how can i monitor loading of specific extensions?

    - by ufk
    Hiya. I'm installing VoodooHDA extension in order for Intel 82801I (ICH9 Family) HD Audio 8086:293E sound card to operate. The sound card does not work but i have no idea how to debug the issue. How can I check if the module was loaded properly? how can i make sure that there where no conflicts? how can i make sure that there were no dependencies issues with another module? Using snow leopard 64 bit. thanks!

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  • Not able to find scripts present in /etc/profile.d directory [on hold]

    - by priya
    I am using Red Hat Linux 6.0 ... using davinchi board. I have to change system clock resolution so I am changing (HZ) env var. For this I have written script so that I can change HZ = 1000 n insert that script in /etc/profile.d and write code for loop in /etc/profile so that while running as usual /etc/profile can load the scripts present in /etc/profile.d. But when I am logging into the system at root level then showing error as "-bash: ./etc/profile.d/resolution.sh(my script name): No such file or directory Also here why it is showing ./etc and not /etc . Is something related to that?? Also I tried to add script in /etc/init.d but still no change in value of HZ takes place. Please tell where to change so that this env var can get changed. The script(resolution.sh) written has :- #!/bin/bash export HZ=1000 The content of /etc/profile which I entered is: if [ -d /etc/profile.d ]; then for i in /etc/profile.d/*.sh; do if [ -r $i ]; then .$i fi done unset i fi And the output of grep command is -rw-r--r-- 1 root root 535 Feb 4 2004 profile -rwxr-xr-x 2 root root 4096 Feb 2 2004 profile.d

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  • "Possible SYN flooding" in log despite low number of SYN_RECV connections

    - by al4
    Recently we had an apache server which was responding very slowly due to SYN flooding. The workaround for this was to enable tcp_syncookies (net.ipv4.tcp_syncookies=1 in /etc/sysctl.conf). I posted a question about this here if you want more background. After enabling syncookies we started seeing the following message in /var/log/messages approximately every 60 seconds: [84440.731929] possible SYN flooding on port 80. Sending cookies. Vinko Vrsalovic informed me that this means the syn backlog is getting full, so I raised tcp_max_syn_backlog to 4096. At some point I also lowered tcp_synack_retries to 3 (down from the default of 5) by issuing sysctl -w net.ipv4.tcp_synack_retries=3. After doing this, the frequency seemed to drop, with the interval of the messages varying between roughly 60 and 180 seconds. Next I issued sysctl -w net.ipv4.tcp_max_syn_backlog=65536, but am still getting the message in the log. Throughout all this I've been watching the number of connections in SYN_RECV state (by running watch --interval=5 'netstat -tuna |grep "SYN_RECV"|wc -l'), and it never goes higher than about 240, much much lower than the size of the backlog. Yet I have a Red Hat server which hovers around 512 (limit on this server is the default of 1024). Are there any other tcp settings which would limit the size of the backlog or am I barking up the wrong tree? Should the number of SYN_RECV connections in netstat -tuna correlate to the size of the backlog? Update As best I can tell I'm dealing with legitimate connections here, netstat -tuna|wc -l hovers around 5000. I've been researching this today and found this post from a last.fm employee, which has been rather useful. I've also discovered that the tcp_max_syn_backlog has no effect when syncookies are enabled (as per this link) So as a next step I set the following in sysctl.conf: net.ipv4.tcp_syn_retries = 3 # default=5 net.ipv4.tcp_synack_retries = 3 # default=5 net.ipv4.tcp_max_syn_backlog = 65536 # default=1024 net.core.wmem_max = 8388608 # default=124928 net.core.rmem_max = 8388608 # default=131071 net.core.somaxconn = 512 # default = 128 net.core.optmem_max = 81920 # default = 20480 I then setup my response time test, ran sysctl -p and disabled syncookies by sysctl -w net.ipv4.tcp_syncookies=0. After doing this the number of connections in the SYN_RECV state still remained around 220-250, but connections were starting to delay again. Once I noticed these delays I re-enabled syncookies and the delays stopped. I believe what I was seeing was still an improvement from the initial state, however some requests were still delayed which is much worse than having syncookies enabled. So it looks like I'm stuck with them enabled until we can get some more servers online to cope with the load. Even then, I'm not sure I see a valid reason to disable them again as they're only sent (apparently) when the server's buffers get full. But the syn backlog doesn't appear to be full with only ~250 connections in the SYN_RECV state! Is it possible that the SYN flooding message is a red herring and it's something other than the syn_backlog that's filling up? If anyone has any other tuning options I haven't tried yet I'd be more than happy to try them out, but I'm starting to wonder if the syn_backlog setting isn't being applied properly for some reason.

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  • Journaled filesystems and power failure

    - by Yoga
    I heard that even a journaled filesystems such as EXT3/EXT4 might corrupted during power failure, e.g. from wikipedia [1]: In the event of a system crash or power failure, such file systems are quicker to bring back online and less likely to become corrupted. Can anyone provide more detail by giving examples such that when corruption can occur corruption is avoided by journaled filesystems [1] http://en.wikipedia.org/wiki/Journaling_file_system

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  • ps aux as non-root doesn't show all processes

    - by JMW
    hi, i'm using an ubuntu 10.04 server... when i run ps aux as root i see all processes when i run ps aux as nonroot i see JUST the processes of the current user after a bit of research i found the following solution: root@m85:~# ls -al /proc/ total 4 dr-xr-xr-x 122 root root 0 2010-12-23 14:08 . drwxr-xr-x 22 root root 4096 2010-12-23 13:30 .. dr-x------ 6 root root 0 2010-12-23 14:08 1 dr-x------ 6 root root 0 2010-12-23 14:08 10 dr-x------ 6 root root 0 2010-12-23 14:08 1212 dr-x------ 6 root root 0 2010-12-23 14:08 1227 dr-x------ 6 root root 0 2010-12-23 14:08 1242 dr-x------ 6 zabbix zabbix 0 2010-12-24 23:52 12747 [...] my first idea was, that it got mounted in a weird way: /etc/fstab is ok and it doesn't seem to be mounted in an weird way... my second idea was, that there might be a rootkit: but it's not a rootkit... rkhunter tells me, that there is no rootkit installed... i don't know if it is since the machine got installed or came with an update. i've just installed zabbix-agent on the machine and realized, that it didn't work properly... What could have caused such strange permissions (500) and how can i set it back to an normal level (555) ? Crazy, i've never seen something like that... thanks in advance for any help and merry christmas :) see you

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