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Compressing images in PDF files
by Jason White 25 Oct '12

25 Oct '12

How can I most effectively compress scanned page images in PDF files without unduly degrading the visual quality? I've been trying it with ImageMagick and a file that I want to compress, but so far without achieving much compression. The ImageMagick identify command, applied to one of the original pages shows: PDF 595x842 595x842+0+0 16-bit Bilevel DirectClass 63.2KB 0.000u 0:00.009 I've been experimenting a little with the -compress, -density and -quality commands of the convert command, but without as much progress as I would prefer. In most cases the output is larger than the input.

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gentoo Xorg: NVIDIA could not open the device file /dev/nividia0
by brettawiggins＠tpg.com.au 23 Oct '12

23 Oct '12

Hi Everyone, I'm having some problems getting Xorg working on my gentoo install. I've started a thread on the gentoo forums, I haven't received any replies since Friday. the link is located here; https://forums.gentoo.org/viewtopic-t-939876.html Basically I have been following the gentoo handbook; http://www.gentoo.org/doc/en/handbook/handbook-amd64.xml the Xorg guide; http://www.gentoo.org/doc/en/xorg-config.xml and the NVIDIA guide; http://www.gentoo.org/doc/en/nvidia-guide.xml When I type 'startx' after installing and configuring everything to use the NVIDIA binary blob (using both root and my normal user) I get the following output NVIDIA: could not open the device file /dev/nvidia0 (input/output error) Fatal server error: no screens found. This is not the first gentoo install I have done. But it is the first one where I have come across this error. My Xorg.0.log is located below; http://bpaste.net/show/51733/ /var/log/messages; http://bpaste.net/show/51739/ ANd finally my /etc/X11/xorg.conf; http://bpaste.net/show/51732/ I have tried everything that was suggested on the forums but still no dice. >From the log files it seems that the Xorg server is having trouble opening the device file /dev/nvidia0.. I could be wrong though.. Any help would be appreciated. Brett.

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Books for LUV library or free to a good home.
by Andrew Greig 22 Oct '12

22 Oct '12

Hi, I have "Running Linux" Fourth Edition and "Linux System Administration" 2001 which I no longer need, both are in good condition, I am moving home so my options are: 1 LUV library 2 Free to a good home 3 In the bin I am happy to bear the cost of postage. Andrew Greig

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Books for LUV library or free to a good home.
by Andrew Greig 22 Oct '12

22 Oct '12

Hi, I have "Running Linux" Fourth Edition and "Linux System Administration" 2001 which I no longer need, both are in good condition, I am moving home so my options are: 1 LUV library 2 Free to a good home 3 In the bin I am happy to bear the cost of postage. Andrew Greig

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getting video resolution
by Russell Coker 21 Oct '12

21 Oct '12

Is there any good way to get the resolution of a video file? For jpegs ImageMagick has the "identify" command which works really well, I'd like to have something similar for movies, particularly flv files. Currently I use the below shell script which is ugly but works, unfortunately it flashes up an X window and probably doesn't work if you aren't using X. #!/bin/sh while [ "$1" != "" ]; do echo q| mplayer $1 2>&1|grep ^VO.*x11| sed -e s/\ =.*$// -e s/^.*\ // shift done -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

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log compression
by Russell Coker 21 Oct '12

21 Oct '12

Does it make sense to compress log files nowadays? BTRFS and ZFS have compression built in, that compression probably won't be as good as gzip on a large file because the filesystems will use smaller block sizes. But it will still provide some benefit. On modern systems writes are more of an issue. Rewriting every log file every night contributes to the wear of SSDs for no real benefit (any system which has log files any fraction of the size of a 60G minimal SSD will probably use ZFS or BTRFS on some big disks for main storage). It seems to me that the default log compression has more problems than benefits with today's technology. It made a lot of sense when 1G was a big hard drive, but nowadays a 60G SSD is about as small as you can buy. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

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flashing a Samsung Galaxy S
by Russell Coker 18 Oct '12

18 Oct '12

http://wiki.cyanogenmod.com/wiki/Samsung_Galaxy_S:_Full_Update_Guide I've got a Galaxy S that I want to use for Cyanogenmod. I went through the part of the above that starts with "assumes the Samsung Galaxy S already has Android 2.3" while my phone had Android 2.2. The result is that it just flashes on the kernel boot screen. I can still get into download mode so all is not lost (yet). http://www.samfirmware.com/WEBPROTECT-i9000.htm I tried getting other zImage files from the above, I tried the 2011 March copy of Android 2.2 from the "America Australia Samsung I9000 Firmwares" section of the above. http://www.samfirmware.com/apps/blog/show/8512833-android-2-3-5-for-galaxy-… I also tried the 2.3.5 from the above. Neither worked. Any suggestions on what I should try next? The phone came from Optus and was running Android 2.2 when I got it. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

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cache, Xen, and zfsonlinux
by Russell Coker 18 Oct '12

18 Oct '12

I'm looking at converting some Xen servers to ZFS. This includes a couple of servers for a reasonable size mail store (8,000,000 files and 600G of Maildir storage). For much of the Xen on ZFS stuff I'll just use zvols for block devices and then use regular Linux filesystems such as Ext3 inside them. This isn't particularly efficient but for most DomUs it doesn't matter at all. Most of the DomUs have little disk access as they don't do much writing and have enough cache to cover most reads. For the mail spool a zvol would be a bad idea, fsck on a 400G Ext3/4 filesystem is a bad thing and having the double filesystem overhead of Ext3/4 on top of a zvol is going to suck for the most disk intensive filesystem. So it seems that the correct solution is to do one of the following: 1) Run the mail store in the Dom0 which will be good for performance at the cost of management. A server which has direct user access in any form (including POP and IMAP) needs to be running all the latest security patches while a Dom0 can have patches delayed if they don't seem relevant to network issues or virtualisation. 2) Use NFS to mount a ZFS filesystem from the Dom0. This will be good for management but there's the problem of caching. I don't think that NFS caches that aggressively so I'd need to give more RAM to the Dom0 for ZFS caching and I'd probably still lose some read performance. 3) Run ZFS in the DomU separately from the Dom0. This will work well for the DomU as long as there is enough RAM. But having a ZFS filesystem in the Dom0 as well as a separate one in the DomU (which would use different partitions of the same disks) would be difficult (ZFS in the Dom0 will probably want to grab all zpools). Also write performance will take a hit if there are two separate zpools on the same disks as there will be seeks between writes - this will be particularly bad for mail delivery where the message and the log entry will be written to different parts of the disk. 4) Run ZFS for mail storage in the DomU and use something other than ZFS for the Dom0. This has the same performance problems as 3) but without the issue of different ZFS instances fighting about it. Also I would lose the support for hashes on the zvol data, I could use files on BTRFS for similar data integrity (I'm using RAID-1 so RAID-Z isn't an option and therefore the benefits of ZFS over BTRFS are fewer) but that would still give performance issues. Any suggestions? -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

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Dovecot/Perdition IMAP session timeout
by Russell Coker 18 Oct '12

18 Oct '12

I have a Dovecot server that gets some old sessions. One back-end server has 5/224 sessions open since September and another 14 from this month that are more than 2 days old. A total of 8.5% of sessions are more than 2 days old. This isn't necessarily a problem on it's own, none of the servers have enough load that 8.5% more or less will matter. But it becomes a problem when a user accumulates enough open and possibly dead sessions over a month that the limit of open sessions is reached and they open a support ticket. It's documented that some MUAs have problems with sessions getting killed, the problems in question can't be that great because no Internet connection is 100% reliable and a significant portion of the user-base doesn't have persistent IP addresses. In my own testing the most I've been able to do is generate a warning message about a session being closed. Is there any reason for not killing the sessions? If there is no good reason not to kill them then is there a way of making Dovecot or Perdition kill a session after it's been IDLE for a couple of days? Otherwise I guess I'll have to use a cron job that kills them. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

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Re: cache, Xen, and zfsonlinux
by Russell Coker 17 Oct '12

17 Oct '12

On Mon, 15 Oct 2012, Daniel Pittman <daniel(a)rimspace.net> wrote: > My fallback would be NFS shared ZFS in the domU - much cheaper because > you only have one ARC, set of checksums, etc, to manage, but with the > added bonus of NFS between the domU and dom0. Fun times. http://wiki.dovecot.org/MainConfig The above page says "Dovecot can also use dnotify, inotify and kqueue to find out immediately when changes occur" in regard to the IMAP "IDLE" command (waiting for notification of new mail). So it seems that using NFS is going to incur extra overhead for polling (which probably isn't that great) as well as delaying the notification of new mail. This probably doesn't matter much as it seems unlikely that there is a reasonable demand by a user for how soon they should be notified which would also involve frequent enough polling to cause significant load. But it is another reason for not using NFS. It's really a pity that the Xen DomU kernel doesn't have it's own filesystem driver which proxies access to the Dom0. Then things like Inotify would just work. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

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