- luv-main - luv.asn.au

fgets() and DOS files
by Russell Coker 31 May '12

31 May '12

Is there a library routine like fgets() but which takes any of CR, NL, and CR+NL as an end of line? -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

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stripping binaries
by Russell Coker 30 May '12

30 May '12

Linux has used demand-loading of executables and shared objects for ages. This means that if an executable or shared object has some pages that happen to never get called (IE for corner conditions that don't happen in the usual case) then they never get read from disk. The same applies for debugging data when the object isn't being debugged. Even if you have unused data on the same pages as executable data thus increasing the number of executable pages loaded into RAM it shouldn't be a big deal as RAM keeps getting bigger so that only a small portion of the multi-gigabytes of RAM in a low-end system is used for executable pages. Disks are getting bigger all the time. Nowadays it would be silly to consider purchasing a disk for a desktop system that's less than 2TB in size and laptops have had hundreds of GB for ages. Currently the biggest root filesystem on a system I run is 12G, that is 0.6% of the space on a desktop disk you might purchase (*) and less than 10% of the low end laptop disks that were on sale a couple of years ago. If I had to make that 24G for the root filesystem it wouldn't be a big deal. In terms of reducing binary size there has been some discussion about a port of Linux that uses 32bit instructions with 64bit data operations and registers on an AMD64 architecture. The idea is to save RAM and TLBs by not using 64/64 while still getting some performance benefits of a 64bit CPU. But there is little interest in this and it seems that Debian won't support it due to no- one caring. So the question is, why strip binaries? Back in the days when we ran servers with 100MB hard drives there was a real need to save space. When a 128Kb/64Kb ADSL link was considered fast there was a real need to reduce download time. But now that most of us have ADSL links that allow 100KB/s (800Kb/s) UPLOAD speeds and significantly faster download speeds. The thing about the debugging symbol table is that you never know when you will need it. Having it always there seems to have no cost that matters but it can provide significant benefits. So why ship a program or shared object that's stripped? (*) The system in question has a 160G disk I got from a junk pile. But as half the disk space is on my /junk filesystem and there is still unallocated space I think this supports my general point. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

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Re: limit concurrent connections with squid
by Tim Connors 30 May '12

30 May '12

On Wed, 30 May 2012, Trent W. Buck wrote: > I suppose there are caveats: it would have to be pleasant, like > OpenWRT, not like a Thecus NAS; and I'd have a strong preference for a Funny you should say that. I ended up giving up on the godawful hacked up scripts (that recursively run chmod/chown immediately on any external drive plugged in, without asking the user) in my thecus n4200, and installed debian on it. I've been meaning to write a blog post on it, if nothing else other than to say "don't buy thecus unless you're prepared to put a lot of work in". -- Tim Connors

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limit concurrent connections with squid
by James Harper 30 May '12

30 May '12

I have a Linksys SRW2048 switch and the UI fails under IE[789] because it uses too many concurrent connections for the switch to handle. I can use IETab in Firefox which works because it indirectly limits the number of concurrent HTTP requests, but that isn't always a solution. I have a squid proxy running on a linux router though, so I was hoping I could limit the number of concurrent connections. The docs tell me I can limit them by using a deny but that will result in the connection failing rather than simply being delayed until other connections are complete. Any suggestions? I'll use netfilter to drop new connection requests if I can't figure it out using squid. Thanks James

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Virtual Box
by Andrew Greig 29 May '12

29 May '12

Hi, I have installed Virtual Box using the package manager for Suse 12.1, and I want to load a Win 7 64bit version, so I set up the Win7 VM but when I try to run it I get this error: Could not start the VM 0x80bb0005 (Could not launch a process for the machine 'Windows 7 (64 bit)' (VERR_ACCESS_DENIED)) What do I need to do to overcome this problem, please? Andrew Greig

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LVM snapshots - incremental to remote?
by Peter Ross 29 May '12

29 May '12

Hi all, I am using ZFS and "zfs snapshot/send/receive", to send ZFS snapshots to a "mirroring" server, just the incremental changes instead of the full snapshot everytime. I am aware of LVM snapshots but I never used it for incremental mirroring (and did not use them a lot, anyway, so I never looked too much under the hood - maybe I should have..) The kernel documentation makes me wonder whether it is possible to achieve the same with LVM: http://www.mjmwired.net/kernel/Documentation/device-mapper/snapshot.txt According to that, you have access to the COW storage as well: # lvcreate -L 1G -n base volumeGroup # lvcreate -L 100M --snapshot -n snap volumeGroup/base # ls -lL /dev/mapper/volumeGroup-* 93 brw------- 1 root root 254, 11 29 ago 18:15 /dev/mapper/volumeGroup-base-real 94 brw------- 1 root root 254, 12 29 ago 18:15 /dev/mapper/volumeGroup-snap-cow 95 brw------- 1 root root 254, 13 29 ago 18:15 /dev/mapper/volumeGroup-snap 96 brw------- 1 root root 254, 10 29 ago 18:14 /dev/mapper/volumeGroup-base 97 Is it possible to send copies of it to a remote server and apply the changes as described in the doc, using the merge options? The idea is to establish a "rotation regime" and just to send the -cow block device for continuous mirroring. Volker Grabsch, on a German mailing list, wrote about his improved "block-level rsync", https://github.com/vog/bscp He plans to use it for LVM mirroring. I just wondered whether he really has to search the whole block device for changes, if LVM knows about them already. Regards Peter

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Audio recording
by Mark Trickett 27 May '12

27 May '12

Hello All, I have a turntable with both analog and streaming USB outputs. It is one from Jaycar. What audio packages do I need to be able to record the streaming USB on Ubuntu and Debian? I have been looking, and there are vague references in the comments about recording, but not specifically stating that they can capture from USB. There is a CD of Windows software, and I am hoping that I do not need to enable something first from a Windows box. That is a SNAFU about which I do not yet have information, but will be looking at. I am thinking along the lines of some USB devices with the software distributed as files on the storage side, but flippable into an "active" device mode, such as some wireless "modems". Regards, Mark Trickett

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multiple atomic lvm snapshots
by James Harper 23 May '12

23 May '12

I have a windows VM running under Xen, and want to take snapshots of all the LV's it is using as it's physical disks, eg: vg0/lv0 - OS vg0/lv1 - FILESTREAM data vg1/lv2 - Databases vg2/lv3 - Database Logs vg's 0, 1, and 2 are on different sets of spindles to give higher IOPS. The problem is that the 4 snapshots need to be created atomically or else I'm going to get my database and transaction logs out of sync as there could be a few ms between the snapshot of lv2 and lv3. I think this isn't possible based on the documentation I've read, but maybe someone here knows different? Being Windows, I can use VSS to fudge it, but making an automatic procedure to do that in conjunction with LVM is more complicated than I want to think about right now! Thanks James

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IP gurus - TCP route cache clobbers IPsec xfrm
by Richard Andrews 21 May '12

21 May '12

I'm load testing a kernel mode IPsec setup. When IKE SAs renegotiate one or two IP packets get sent on the default route but after the tunnel is back up the TCP connection remains stuck on the default route by-passing xfrm policy until the TCP connection closes from retransmission failures. Ping is not affected the same way. It uses the tunnel as soon as a new child SA is up (even while TCP is broken). The next TCP connection uses the tunnel immediately. What can I do to fix this? Things I've tried that did not work: - conntrack -D - iptables -t raw ... -j NOTRACK # have verified the connections never appear in conntrack state - ip route cache flush # while a connection is stuck on the wrong path Kernel is 2.6.32. The TCP connections terminate on a loopback of the IPsec gateway. Ideas?

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grub init /bin/bash
by Colin Fee 21 May '12

21 May '12

A work colleague was reading a blog and in one of the comments was a statement saying that if you append init=/bin/bash to the grub boot line e.g. linux /vmlinuz-3.2.0-2-amd64 root=UUID=26585ddb-7dde-4a7e-b2c7-e32330bb4cc8 ro splash quiet init=/bin/bash you end up ia a shell with root privileges. So we had go at it and it works. We even tried booting with a USB tick in place to see if you could copy stuff to it and you can. The question that arose was what about network access? Do you have it? i.e. is there a tcp/ip stack running and if not how would you load one etc? -- Colin Fee tfeccles(a)gmail.com

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