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Getting the return value of the last command run
by Dotan Cohen 31 May '11

31 May '11

All commands return a value, usually 0 if run properly. For instance, try: $ ls && echo "done" $ lsd && echo "done" The echo command is only executed if the ls command exited successfully. If one did not add the echo command with the && after a command, how can he determine if the command exited successfully? I have a particularly troubling script that gives does not mention if it exits successfully or not. I could modify it (and probably will some day) but in general I'd like to know the answer to this question as a learning experience. Thanks. -- Dotan Cohen http://gibberish.co.il http://what-is-what.com

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scheduling differences between CentOS 4 and CentOS 5?
by Matt Garman 30 May '11

30 May '11

We have several latency-sensitive "pipeline"-style programs that have a measurable performance degredation when run on CentOS 5.x versus CentOS 4.x. By "pipeline" program, I mean one that has multiple threads. The mutiple threads work on shared data. Between each thread, there is a queue. So thread A gets data, pushes into Qab, thread B pulls from Qab, does some processing, then pushes into Qbc, thread C pulls from Qbc, etc. The initial data is from the network (generated by a 3rd party). We basically measure the time from when the data is received to when the last thread performs its task. In our application, we see an increase of anywhere from 20 to 50 microseconds when moving from CentOS 4 to CentOS 5. I have used a few methods of profiling our application, and determined that the added latency on CentOS 5 comes from queue operations (in particular, popping). However, I can improve performance on CentOS 5 (to be the same as CentOS 4) by using taskset to bind the program to a subset of the available cores. So it appers to me, between CentOS 4 and 5, there was some change (presumably to the kernel) that caused threads to be scheduled differently (and this difference is suboptimal for our application). While I can "solve" this problem with taskset, my preference is to not have to do this. I'm hoping there's some kind of kernel tunable (or maybe collection of tunables) whose default was changed between versions. Anyone have any experience with this? Perhaps some more areas to investigate? Thanks, Matt

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Re: [CentOS] Where is the Centos Linux 5.5 kernel syscall handler for mmap?
by Keith Roberts 30 May '11

30 May '11

Hi. Sorry for the late reply, but I did not get the message that was archived. I stumbled upon it here: http://osdir.com/ml/centos/2011-05/msg01193.html All I got was this message: I am out of the office until 06/11/2011. I will be out of the office starting 5/27/2011 and will not return until 6/12/2011. I will respond to your message when I return. Note: This is an automated response to your message "CentOS Digest, Vol 76, Issue 28" sent on 5/28/2011 9:00:02 AM. This is the only notification you will receive while this person is away. In response to your question: "Thank you for your suggestion about doing a grep of the source code. We found mmap.S in ../sysdeps/unix/sysv/linux/i386. We looked in mmap.S and found a lot of assembly code. Could you please tell us if any of the assembly code call the kernel syscall handler for mmap.s? Also, we ran make for the kernel Makefile and we obtained the following result shown below. Could you please suggest us how to fix the kernel Makeconfig so that it skips over libc_pic.os? Thank you for your help." May I suggest you join the LKML? http://www.kernel.org/pub/linux/docs/lkml/ I'm sure they are alot more knowledgeable concerning things like tweaking the internals of the Linux kernel. HTH Kind Regards, Keith Roberts ----------------------------------------------------------------- Websites: http://www.karsites.net http://www.php-debuggers.net http://www.raised-from-the-dead.org.uk All email addresses are challenge-response protected with TMDA [http://tmda.net] -----------------------------------------------------------------

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Re: [CentOS] OT: Why VM?
by James B. Byrne 30 May '11

30 May '11

On Fri, May 27, 2011 14:36, Jack Bailey wrote: > There are lots of good reasons to virtualize. > > http://www.vmware.com/virtualization/why-virtualize.html > > Jack > As it turns out, that was one of the net resources I had in mind when I described what I found as mostly puff and smoke. This is what this site claims as advantages to VM: > Top 5 Reasons to Adopt Virtualization Software > 1. Get more out of your existing resources: Pool common > infrastructure resources and break the legacy one application > to one server model with server consolidation. I have difficulty with this statement on so many levels that it is hard to know where to begin. Perhaps the most egregious is the mindless equating of server with host. What measurable benefits accrue to a firm from 'breaking the legacy', whatever that means. > 2. Reduce data center costs by reducing your physical > infrastructure and improving your server to admin ratio: > Fewer servers and related IT hardware means reduced real > estate and reduced power and cooling requirements. Better > management tools let you improve your server to admin ratio > so personnel requirements are reduced as well. Personally, my experience is that, if anything, running multiple systems on a vm host measurably increases the administrative burden per host. For one thing, you now have multiple instances to update and to keep secure whereas before you had one OS to worry about. If we had tens or hundreds or thousands of servers then yes, I can see the benefits. We, however, do not deal with equipment on that scale. > 3. Increase availability of hardware and applications for > improved business continuity: Securely backup and migrate > entire virtual environments with no interruption in service. > Eliminate planned downtime and recover immediately from > unplanned issues. I suppose that moving VM instances as file systems provides a real value by eliminating the setup and configuration required to get bare metal to flash up in a usable fashion. This is in fact the only area that I see a real advantage to VM over bare metal installs. > 4. Gain operational flexibility: Respond to market changes with > dynamic resource management, faster server provisioning and > improved desktop and application deployment. I have no idea how deploying VMs to a company's desktop workstations could possibly benefit the firm., > 5. Improve desktop manageability and security: Deploy, manage > and monitor secure desktop environments that users can access > locally or remotely, with or without a network connection, on > almost any standard desktop, laptop or tablet PC. Again, how is this accomplished and what are the advantages over a single OS install? None of the above claims have anything to do with VM per se as far as I can see. -- *** E-Mail is NOT a SECURE channel *** James B. Byrne mailto:ByrneJB@Harte-Lyne.ca Harte & Lyne Limited http://www.harte-lyne.ca 9 Brockley Drive vox: +1 905 561 1241 Hamilton, Ontario fax: +1 905 561 0757 Canada L8E 3C3

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PHP Source
by Ron Young 30 May '11

30 May '11

I have a pressing need to compile a utility called odbtp into php on my new 64 bit machine with an AMD chip that is currently running CentOS 5.6. Where can I find the source files for the CentOS recommended versions of php. I have searched the CentOS and related repository sites and can find php in several places but not the source files. Thanks in advance. Regards, Ron Young 919-621-9015 http://www.linkedin.com/in/ronhyoung +++++++++++++++++++ Little tiny dreams require little tiny thoughts and little tiny steps. Great big dreams require great big thoughts and little tiny steps. +++++++++++++++++++ *Kosh*: The avalanche has already started. It is too late for the pebbles to vote.

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local repo
by Jerry Geis 30 May '11

30 May '11

Hi all, When I am installing I use kickstart and have a line like: repo --name=Updates --baseurl=http://192.168.1.14/centos/5.6/updates/x86_64/ and that works great for installing the OS. After that the machine reboots and I have it automatically go into additional installations running scripts. These installations do "yum install XXX". However, its no longer using my above repo its using the mirrorlist (as expected). My questions are : 1) I dont see a way in yum to say "use this repo to install", is there a way to point to my server in the office and dont do the mirrorlist. 2) Do I just drop a file called CentOS-office in the /etc/yum.repos.d directory that looks like this and it will be used first instead of the mirrorlist: [base] name=CentOS-$releasever - Base mirrorlist=http://192.168.1.14/?release=$releasever&arch=$basearch&repo=os #baseurl=http://192.168.1.14/centos/$releasever/os/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5 #released updates [updates] name=CentOS-$releasever - Updates mirrorlist=http://192.168.1.14/?release=$releasever&arch=$basearch&repo=updates #baseurl=http://192.168.1.14/centos/$releasever/updates/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5 I dont want to mess anything up and I want additional package installs in the office to go faster in the office. I can remove the file when I am done installing. Is there a better way or is this the way to do it? jerry

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OT: Why VM?
by James B. Byrne 30 May '11

30 May '11

I have been working off and on with Xen and KVM on a couple of test hosts for that past year or so and while now everything seems to function as expected, more or less, I find myself asking the question: Why? We run our own servers at our own sites for our own purposes. We do not, with a few small exceptions, host alien domains. So, while rapidly provisioning or dynamically expanding a client's vm might be very attractive to a public hosting provider that is not our business model at all. Why would a small company not in the public hosting business choose to employ VM technology? What are the benefits over operating several individual small form factor servers or blades instead? I am curious because what I can find on the net respecting VM use cases, outside of for public providers or application testing, seems to me mostly puff and smoke. This might be considered OT but since CentOS is what we use it seems to me best that I ask here to start. -- *** E-Mail is NOT a SECURE channel *** James B. Byrne mailto:ByrneJB@Harte-Lyne.ca Harte & Lyne Limited http://www.harte-lyne.ca 9 Brockley Drive vox: +1 905 561 1241 Hamilton, Ontario fax: +1 905 561 0757 Canada L8E 3C3

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Re: [CentOS] Where is the Centos Linux 5.5 kernel syscall handler for mmap? (Keith Roberts)
by Frank Chang 29 May '11

29 May '11

Keith Roberts, Thank you for your suggestion about doing a grep of the source code. We found mmap.S in ../sysdeps/unix/sysv/linux/i386. We looked in mmap.S and found a lot of assembly code. Could you please tell us if any of the assembly code call the kernel syscall handler for mmap.s? Also, we ran make for the kernel Makefile and we obtained the following result shown below. Could you please suggest us how to fix the kernel Makeconfig so that it skips over libc_pic.os? Thank you for your help. gcc -shared -static-libgcc -Wl,-O1 -Wl,-z,defs -Wl, -dynamic-linker=/home/frankc/DQT1/glibc-2.9/lib/ld-linux.so.2 -B/home/frankc/DQTTest5/csu/ -Wl, --version-script=/home/frankc/DQTTest5/libc.map -Wl,-soname=libc.so.6 -Wl,-z,combreloc -Wl,-z,relro -Wl,--hash-style=both -nostdlib -nostartfiles -e __libc_main -L/home/frankc/DQTTest5 -L/home/frankc/DQTTest5/math -L/home/frankc/DQTTest5/elf -L/home/frankc/DQTTest5/dlfcn -L/home/frankc/DQTTest5/nss -L/home/frankc/DQTTest5/nis -L/home/frankc/DQTTest5/rt -L/home/frankc/DQTTest5/resolv -L/home/frankc/DQTTest5/crypt -L/home/frankc/DQTTest5/nptl -Wl, -rpath-link=/home/frankc/DQTTest5:/home/frankc/DQTTest5/math:/home/frankc/DQTTest5/elf: /home/frankc/DQTTest5/dlfcn:/home/frankc/DQTTest5/nss:/home/frankc/DQTTest5/nis: /home/frankc/DQTTest5/rt:/home/frankc/DQTTest5/resolv:/home/frankc/DQTTest5/crypt: /home/frankc/DQTTest5/nptl -o /home/frankc/DQTTest5/libc.so -T /home/frankc/DQTTest5/shlib.lds /home/frankc/DQTTest5/csu/abi-note.o /home/frankc/DQTTest5/elf/soinit.os /home/frankc/DQTTest5/libc_pic.os / home/frankc/DQTTest5/elf/sofini.os /home/frankc/DQTTest5/elf/interp.os /home/frankc/DQTTest5/elf/ld.so -lgcc /home/frankc/DQTTest5/libc_pic.os: In function `__libc_fork': /home/frankc/DQT1/glibc-2.9/posix/../nptl/sysdeps/unix/sysv/linux/i386/../fork.c:79: undefined reference to `__sync_bool_compare_and_swap_4' /home/frankc/DQTTest5/ gcc -shared -static-libgcc -Wl,-O1 -Wl,-z,defs -Wl, -dynamic-linker=/home/frankc/DQT1/glibc-2.9/lib/ld-linux.so.2 -B/home/frankc/DQTTest5/csu/ -Wl, --version-script=/home/frankc/DQTTest5/libc.map -Wl,-soname=libc.so.6 -Wl,-z,combreloc -Wl,-z,relro -Wl,--hash-style=both -nostdlib -nostartfiles -e __libc_main -L/home/frankc/DQTTest5 -L/home/frankc/DQTTest5/math -L/home/frankc/DQTTest5/elf -L/home/frankc/DQTTest5/dlfcn -L/home/frankc/DQTTest5/nss -L/home/frankc/DQTTest5/nis -L/home/frankc/DQTTest5/rt -L/home/frankc/DQTTest5/resolv -L/home/frankc/DQTTest5/crypt -L/home/frankc/DQTTest5/nptl -Wl, -rpath-link=/home/frankc/DQTTest5:/home/frankc/DQTTest5/math:/home/frankc/DQTTest5/elf: /home/frankc/DQTTest5/dlfcn:/home/frankc/DQTTest5/nss:/home/frankc/DQTTest5/nis: /home/frankc/DQTTest5/rt:/home/frankc/DQTTest5/resolv:/home/frankc/DQTTest5/crypt: /home/frankc/DQTTest5/nptl -o /home/frankc/DQTTest5/libc.so -T /home/frankc/DQTTest5/shlib.lds /home/frankc/DQTTest5/csu/abi-note.o /home/frankc/DQTTest5/elf/soinit.os /home/frankc/DQTTest5/libc_pic.os / home/frankc/DQTTest5/elf/sofini.os /home/frankc/DQTTest5/elf/interp.os /home/frankc/DQTTest5/elf/ld.so -lgcc /home/frankc/DQTTest5/libc_pic.os: In function `__libc_fork': /home/frankc/DQT1/glibc-2.9/posix/../nptl/sysdeps/unix/sysv/linux/i386/../fork.c:79: undefined reference to `__sync_bool_compare_and_swap_4' /home/frankc/DQTTest5/libc_pic.os: In function `__nscd_drop_map_ref': /home/frankc/DQT1/glibc-2.9/nscd/nscd-client.h:320: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os: In function `nscd_getpw_r': /home/frankc/DQT1/glibc-2.9/nscd/nscd_getpw_r.c:232: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os: In function `__nscd_drop_map_ref': /home/frankc/DQT1/glibc-2.9/nscd/nscd-client.h:320: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os: In function `nscd_getgr_r': /home/frankc/DQT1/glibc-2.9/nscd/nscd_getgr_r.c:321: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os: In function `__nscd_drop_map_ref': /home/frankc/DQT1/glibc-2.9/nscd/nscd-client.h:320: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os:/home/frankc/DQT1/glibc-2.9/nscd/nscd_gethst_r.c:400: more undefined references to `__sync_fetch_and_add_4' follow /home/frankc/DQTTest5/libc_pic.os: In function `__nscd_get_map_ref': /home/frankc/DQT1/glibc-2.9/nscd/nscd_helper.c:431: undefined reference to `__sync_val_compare_and_swap_4' /home/frankc/DQTTest5/libc_pic.os: In function `*__GI___libc_freeres': /home/frankc/DQT1/glibc-2.9/malloc/set-freeres.c:39: undefined reference to `__sync_bool_compare_and_swap_4' collect2: ld returned 1 exit status : In function `__nscd_drop_map_ref': /home/frankc/DQT1/glibc-2.9/nscd/nscd-client.h:320: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os: In function `nscd_getpw_r': /home/frankc/DQT1/glibc-2.9/nscd/nscd_getpw_r.c:232: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os: In function `__nscd_drop_map_ref': /home/frankc/DQT1/glibc-2.9/nscd/nscd-client.h:320: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os: In function `nscd_getgr_r': /home/frankc/DQT1/glibc-2.9/nscd/nscd_getgr_r.c:321: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os: In function `__nscd_drop_map_ref': /home/frankc/DQT1/glibc-2.9/nscd/nscd-client.h:320: undefined reference to `__sync_fetch_and_add_4' /home/frankc/DQTTest5/libc_pic.os:/home/frankc/DQT1/glibc-2.9/nscd/nscd_gethst_r.c:400: more undefined references to `__sync_fetch_and_add_4' follow /home/frankc/DQTTest5/libc_pic.os: In function `__nscd_get_map_ref': /home/frankc/DQT1/glibc-2.9/nscd/nscd_helper.c:431: undefined reference to `__sync_val_compare_and_swap_4' /home/frankc/DQTTest5/libc_pic.os: In function `*__GI___libc_freeres': /home/frankc/DQT1/glibc-2.9/malloc/set-freeres.c:39: undefined reference to `__sync_bool_compare_and_swap_4' collect2: ld returned 1 exit status

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AUTO: Ott, Jerry is out of the office. (returning 06/11/2011)
by JOtt＠semtech.com 28 May '11

28 May '11

I am out of the office until 06/11/2011. I will be out of the office starting 5/27/2011 and will not return until 6/12/2011. I will respond to your message when I return. Note: This is an automated response to your message "CentOS Digest, Vol 76, Issue 28" sent on 5/28/2011 9:00:02 AM. This is the only notification you will receive while this person is away.

1 0

Where is the Centos Linux 5.5 kernel syscall handler for mmap?
by Frank Chang 28 May '11

28 May '11

Good evening, We are using Centos Linux Release 5.5 x86_32. We wondering where the kernel syscall handler for mmap in Centos Linux 5.5 distribution is located(for example /usr/xxx/....)? Would any programmers or operating system administrators have this information? Thank you.

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