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142

IPTables isnt made for this kind of work, where lots and lots of packets need to be analyzed to make these decisions. IPTables is partly the answer though! The real answer to this is the awesome and underused traffic control facilities in linux. Note that mucking around with this without knowing what is going on may lead to you losing network connectivity ...


17

READ. YOUR. CONFIGS. And when that fails... READ. ALL. OUTPUTS. Do you see what's in ifcfg-bond0? No, do you understand what's in ifcfg-bond0? What in the world of slippery penguins is miimmon=100? Oh I'm sorry, did you mean miimon=100? Yeah, I think you meant miimon and not miimmon. Also, a big giveaway is that when you restart your network service ...


12

We recommend everyone run through a reinstall rather than attempt an inplace upgrade from CentOS-4 or CentOS-5! Source: http://lists.centos.org/pipermail/centos-announce/2011-July/017645.html You can run this upgrade centos6 just by using yum upgrade --enablerepo=centosplus. Do not forget: each system running centos is individual (!). I recommend ...


12

Put them in /etc/sysconfig/network-scripts/ifcfg-eth0, with a 2 or 3 etc. after them, such as: IPADDR2=192.0.2.48 NETMASK2=255.255.255.0 IPADDR3=192.0.2.49 NETMASK3=255.255.255.0 Unfortunately this seems to be undocumented (or I can't find it right now; it looks like Red Hat rearranged their web site yet again).


12

Yes, you have to have an active RHEL subscription to download packages from RHEL's repositories. If your machine has never been subscribed, or the subscription is expired, you will not be able to use any of the repositories provided by RHEL. Red Hat states, in relevant part: If you choose to let all your subscriptions expire and have no other active ...


10

The fix in RHEL6 or in derivatives of RHEL6 is to add the parameter multilib_policy=all in your /etc/yum.conf file and that should work out. It will enable fetching packages of all architectures and is not limited to the 64 bit versions only.


10

I would not recommend downgrading the distribution OpenSSH version shipped with RHEL6. There are dependencies that would potentially break your server. So no, it's probably not okay... We can possibly help you troubleshoot the client's scp issue, though. Have you run the SSH daemon in debug mode? Have you done the same with the client system?


9

Use virsh define somefile.xml and virsh start domain-name, doing this the VM will be persistent. I can't check right now, but I think you can use virsh define on an already started VM and this will make it persistent.


9

Better than fighting with udev to force a device name for a given device, a permanent solution is to use UUIDs. This is valid for any device known to the device-mapper. This way, you don't have to worry if you add extra disks to your host. The UUID identifier guaranties that the right device will be used.


8

Short Answer Install the equivalent centos-release package from a centos downloads location; This will enable the CentOS package repos where you can do a yum update or a yum install gcc Long(er) Answer With respect to the other answers, I felt a slight more full answer could be given to your question. CentOS aims to be 100% binary compatible with RHEL, ...


8

Yes, the tool is called mock and it's in EPEL. Typical usage: rpmbuild -bs mypackage.spec mock -r epel-6-x86_64 mypackage-0.1-1.src.rpm This is actually the preferred way to build RPMs, precisely because it isolates the process from the system so that unexpected dependencies don't get pulled in. You can modify the files in /etc/mock to have it pull in ...


7

Mike, there are generally a few sources of good guides out there for security hardening. The DISA STIGs The NSA SRGs NIST CIS Benchmarks Vendor guidance SANS Books specific to hardening At my work, we use a combination of the DISA STIGs, along with puppet for Linux. I'd be more likely to say that is inadequate and push for some of the recommendations ...


7

run uname -a see which kernel you have running, then use yum remove kernel- (one by one) to all BUT the one that you're running (also keep one extra in addition to the one that you're running just in case if you need to load older kernel for whatever reason)


7

This functionality is provided by rpm, not yum: rpm -ql [packagename] From the documentation: The general form of an rpm query command is rpm {-q | --query} [PACKAGE_NAME] [query-options] Information selection options: -l, --list List files in package.


7

XFS and EL6 have fallen into an ugly state... I've abandoned XFS on EL6 systems for the time being due to several upstream features/changes slipping into the Red Hat kernel... This one was a surprise and caused some panic: Why are my XFS filesystems suddenly consuming more space and full of sparse files? Since November 2012, the XFS version shipping in ...


7

No, it does not. If it's not running, it's merely a file in the file system. If an attacker manages to restart your system with this kernel, he has already full control over the system anyway.


6

You really won't find support for something like this, as it's not something that will pass any sanity checks. So, think about it a bit. Your computer needs to know the gateway address in order to reach other machines outside it's local subnet. So, if you have a subnet 10.0.1.0/24 and your machine is 10.0.1.12, it would be able to reach any machine from ...


6

Delete at least one of the old kernels, as alexus said. Then: Edit /etc/yum.conf and specify the limit of the number of kernel versions to keep. It's set to 5 by default, but your system seems to be capable of handling only two: installonly_limit=2 Finally, complain to the VPS provider about the strange template. /boot is 500MB by default in a CentOS 6 ...


6

Downgrading to an unsupported PHP version is likely to be (no surprise) unsupported. Compiling from source, or finding someone who has packaged an RPM, are pretty much your only two options. BIG IMPORTANT SECURITY NOTE You probably do not need to use dl(). You should never need to use dl(). Despite what you may have been told, alternatives do exist to ...


6

Your system is having some sort of problem with your Red Hat subscription. Make sure you have an active entitlement assigned to the machine, and if you do, contact Red Hat to resolve the problem.


6

rpm -ql packagename is roughly equivalent. You should think of yum as similar to apt-get and rpm as roughly equivalent to dpkg. yum deals with packages in terms of repositories, and rpm deals with individual packages. Ubuntu actually provides a cheat sheet on similar actions: Switching between RedHat and Ubuntu


6

The fix: Apparently, the Oracle installation on this system injected Oracle's path into LD_LIBRARY_PATH... [root@dev1v etc]# export declare -x LD_LIBRARY_PATH="/home/oracle/app/oracle/product/11.2.0/client_1/lib" Unsetting the variable allowed yum to function properly again.


6

It's high because that saves effort. It takes effort to make memory free. And if you do that, it just takes effort to make it used again. So, to save effort, modern operating systems only make memory free if they have absolutely no other choice. If you're thinking "I want memory free now so I can use it later", banish that thought from your mind. Memory ...


6

It's not the voltage regulation that causes the performance problem, but the debugging kernel interrupts that are being triggered by it. Despite some misinformation on Redhat's part, all of the linked pages are referring to the same phenomenon. The voltage regulation happens with or without the Performance profile, likely due to the Turbo Boost feature ...


6

Actually, the command string listed in the sudoers is requiring to be the exact match. In your example, you put the command string /usr/bin/yum update in the sudoers configuration line, but the command you finally executes is yum -y update. (the difference is the extra parameter -y). Then, the mismatch in command string caused the sudoers failed to hit ...


5

The benefits are: more flexibilty if you want to change the size of swap you don`t need a partition for swap AFAIK this - once existing drawback does NOT exist any more: not possible to resume from swap


5

It looks like you've encountered a bug in the version of the kernel included in RHEL. There was a thread about this problem on the Xen development email list last year: http://old-list-archives.xen.org/archives/html/xen-devel/2010-11/msg00616.html You should probably try rebooting your instance via the EC2 console or command line utilities. Regarding the ...


5

Your options for creating filesystems are limited to those described in the kickstart documentation (in particular, the part, logvol, and raid commands). The assumption there is generally that you're happy with the default options when creating filesystems. If you need anything fancier, you'll need to use the %pre or %post section to call mkfs.xfs ...


5

OK, time for something even more drastic! echo 1 >/proc/sys/kernel/panic This instructs the kernel that when you kernel panic, to reboot the host in 1 second. echo c >/proc/sysrq-trigger This forces the kernel to panic. So hopefully you'll end up rebooting the host.


5

As per the recommendation of MadHatter here. I will post my answer here as an addendum to the answers here so that it may be used in conjunction with the answers suggested here. Taken from the following website ## Install yum utils ## yum install yum-utils ## Package-cleanup set count as how many old kernels you want left ## package-cleanup --oldkernels ...



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