/ - rtt - IT Resource

  • Linux What is umask (user mask) for file and directory creation permissions and how to calculate umask and change the defaults


    umask are the default permissions that are applied when a file or directory are created.  To see this in action simply just "touch filename" or "mkdir somedir" and you'll see what default permissions are applied. The first thing I always tell people you should know is to NEVER change the defaults unless you are making them more restrictive.  But they work well and if you change the defaults you could end up creating a file without permission to read........
  • genisoimage errors with long filenames and deep directory structures


    You'll have to violate the iso9660 standards but it is necessary if you want to preserve your filesystem and filenames and shouldn't be an issue as long as you are using a modern OS like Linux. genisoimage -o Backup-Myfiles.iso -r -J -joliet-long  /some/path/ You will get errors like below (even enabling joliet-long didn't help) genisoimage: Error: /some/filename.pdf have the same Joliet name Joliet tree sort failed. The -joliet-lo........
  • Centos PXEBoot NetInstall Failure - Pane is dead


    ValueError: new value non-existent xfs filesystem is not valid as a default fs type Pane is dead From what I read this is misleading and has to do with the fact that the initrd and kernel are mismatched. This is a hard situation because for some older hardware I am using the Centos Plus kernel which has modules that I require for an older server/NIC.  This seems to have cropped up in the past few months and there is no simple fix........
  • ffmpeg Linux Mint download, compile and install howto


    #if you have nvidia make sure you install the nvidia-cuda-toolkit so hardware acceleration can be used wget http://ffmpeg.org/releases/ffmpeg-3.3.2.tar.bz2 tar -jxvf ffmpeg-3.3.2.tar.bz2 cd  ffmpeg-3.3.2/ ./configure --disable-yasm install prefix            /usr/local source path              ........
  • mdadm kernel panic if trying to change --layout on a RAID10


    It is already known this is not possible   mdadm --create /dev/md3 --level 10 --layout=f2 --raid-devices=2 /dev/sdc1 /dev/sdd1 mdadm: /dev/sdc1 appears to be part of a raid array:        level=raid10 devices=2 ctime=Sat Dec 24 18:44:29 2016 mdadm: /dev/sdd1 appears to be part of a raid array:        level=raid10 devices=2 ctime=Sat Dec 24 18:44:29 2016 Continue creating ar........
  • mysql_real_escape_string returns an empty string solution


    This is a common mistake but many people do not realize this function comes from mysql itself, so therefore you need an active mysql connection open. Usually the string will be empty and null when you call it from outside of the database connection portion of your code. eg. an example of the wrong way and creating a null/empty string $var = mysql_real_escape_string($myself) mysql_connect(); // returns n........
  • Centos 6 how to guide convert LVM non-RAID into mdadm 1/10 RAID array live without reinstalling


    Here is the scenario you or a client have a remote machine that was installed as a standard/default minimal Centos 6.x machine on a single disk with LVM for whatever reason.  Often many people do not know how to install it to a RAID array so it is common to have this problem and why reinstall if you don't need to?  In some cases on a remote system you can't easily reinstall without physical or KVM access. So in this case you add a second physical or disk or already ha........
  • esniper and curl errors https://signin.ebay.com/ws/eBayISAPI.dll?SignIn: Couldn't connect to server: couldn't connect to host


    I kept thinking it was esniper but somehow my bash settings have a preset proxy that was creating the issue. https://signin.ebay.com/ws/eBayISAPI.dll?SignIn: Couldn't connect to server: couldn't connect to host curl manually to any URL is the same: curl: (7) couldn't connect to host Run curl with -vvvvvv mode to see the issue: curl -vvvvvvvvvv http://realtechtalk.com * About to c........
  • yum error installing php solution - exclude php from being installed from third party repos


    Error: Package: php-Monolog-dynamo-1.7.0-1.el6.noarch (epel)            Requires: php-aws-sdk Error: php-pecl-zendopcache conflicts with 1:php-eaccelerator-0.9.6.1-1.el6.x86_64 Error: php-xcache conflicts with php-pecl-apc-3.1.9-2.el6.x86_64 Error: php-pecl-zendopcache conflicts with php-pecl-apc-3.1.9-2.el6.x86_64 Error: Package: php-horde-Horde-Vfs-2.1.2-2.el6.noarch (epel)    &n........
  • Gnome Terminal Cannot Open Error "There was an error creating the child process for this terminal" "Failed to create pipe for communicating with child process (Too many open files)"


    There was an error creating the child process for this terminal Failed to create pipe for communicating with child process (Too many open files) I get this when trying to open a new tab or new window even.  I've had far more sessions open (literally dozens) before without getting this error.........
  • Linux Ubuntu Debian Howto Manually Update/Install Thunderbird


    wget http://download-location sudo tar xjvf thunderbird-24.2.0.tar.bz2 -C /opt ln -s /opt/thunderbird/thunderbird /usr/bin/thunderbird [sudo] password for one: ln: creating symbolic link `/usr/bin/thunderbird': File exists sudo rm /usr/bin/thunderbird ln -s /opt/thunderbird/thunderbird /usr/bin/thunderbird The above is how I did it, if you don't do it properly you'll find that you are still using the old version (........
  • Asterisk iptables block bruteforce attacks howto with fail2ban


    yum -y install fail2ban vi /etc/fail2ban/jail.conf [asterisk-tcp] enabled  = true filter   = asterisk action   = iptables-multiport[name=asterisk-tcp, port="5060,5061", protocol=tcp]            sendmail-whois[name=Asterisk, dest=you@example.com, sender=fail2ban@example.com] logpath  = /var/log/asterisk/messages maxret........
  • CPanel suhosin install failed


    /scripts/phpextensionmgr install PHPSuHosin Updating md5sum list Fetching http://httpupdate.cpanel.net/cpanelsync/easy/targz.yaml (connected:0).......(request attempt 1/12)...Resolving httpupdate.cpanel.net...(resolve attempt 1/65)...     Fetching http://httpupdate.cpanel.net/mirror_addr_list (connected:0).......(request attempt 1/3)......connecting to 74.50.120.123...@74.50.120.123......connected......receiving...100%......request success......Done........
  • LSI MegaRAID Adventures, Guide and HowTo


    LSi Megaraid At first it was configured as a RAID 0, then I deleted the Virtual Disk Group. I thought both drives would be shown and detected in Linux as sda and sdb but it actually shows nothing. To make them work you have to hit Ctrl+R before the system boots (when prompted) and create a Virtual Disk Group.  In my case I created each one as RAID 0 (with a single drive only) as I just wanted JBOD but there is no such option or default in these Dell Pe........
  • kvm cannot boot xen guest using lvm


    This booting error is because the Xen PV guest image uses the Xen kernel, this is not compatible with anything but a host running a Xen kernel. I did a kpartx -av virtual.img and then it created some partitions that showed up in fdisk. I mounted it and did a chroot into it and removed the xen kernel and installed a normal kernel but Xen still shows the same kernel in Grub (only the Xen one). This is strange but it seems like this Xen PV guest has some sort of hidden or........
  • KVM/QEMU Base/Template Images and the power they provide


     qemu-img create -b centos.5-8.x86.20120308.qcow2 -f qcow2 ../kvmguests/25000-centos5.8x86.qcow2 Formatting '../kvmguests/25000-centos5.8x86.qcow2', fmt=qcow2, backing_file=centos.5-8.x86.20120308.qcow2, size=10485760 kB -b the source/base image -f format is qcow2 and the location of the destination image What is so special about this?  It's even quicker than creating a template with OpenVZ but this is an actual OS. It saves time a........
  • CPanel error: "Your SSL certificate failed to install on your site."


    This error in my experience is user error although CPanel doesn't help, this message doesn't give you much to go on. Let's talk more about the process of setting up SSL with CPanel. Your site must have a dedicated/non-shared IP to even have the option of creating an SSL Certificate. You must create a Private Key (do not delete this private key!) You must create a CSR ( Certificate Signing Request) Use CSR to create cert........
  • Creating tunnel gives the error ioctl: no such device


    ip tunnel add tun3 mode gre remote 192.58.1.5 ttl 64 ioctl: no such device I solved this on Centos by loading the ip_gre module: modprobe ip_gre On Debian I believe it is the "sit" module.........
  • mdadm how to add a device to an array after a failure


    This array is a RAID 1 and in this case 1 of the 2 drives failed (a WD drive and I've found them to be the weakest and most unreliable of any brand and are easily damaged/DOA when shipping them). mdadm --manage /dev/md0 --add /dev/sdb1 The above assumes the array you want to add to is /dev/md0 and the device we are adding is /dev/sdb1 *One thing to remember is to make sure the partition you are adding is the correct size for the array.  You can also g........
  • mysql enable slow query logging/Query Cache Solution - find/track cause of slow mysqld/high IO/CPU usage


    If you have a webserver and find you have high IO/lagginess MySQL is one of the first things to check.  It turns out MySQL was my problem and it was creating a high load on my server, especially for IO. How to Enable MySQL Slow Query Logging To Find Slow Performance/Queries vi /etc/my.cnf Add this anywhere under [mysqld] #slow queries log-slow-queries = /var/log/mysql/mysqlslowqueries.log long_query_time = 1........
  • MySQL NEVER delete ib_logfile0 or ibdata1 or you'll lose data


    don't delete /var/lib/mysql/ib_logfile0 or ibdata1 or mysql won't restart I didn't realize they were internal and not part of replication like the relay files! /usr/libexec/mysqld: ready for connections. Version: '4.1.22-log'  socket: '/var/lib/mysql/mysql.sock'  port: 3306  Source distribution 110127 16:31:00 [Note] /usr/libexec/mysqld: Normal shutdown 110127 16:31:00  InnoDB: Starting shutdown...........
  • Installing Virtualbox on Centos 5.5


    wget http://download.virtualbox.org/virtualbox/3.2.8/VirtualBox-3.2-3.2.8_64453_rhel5-1.i386.rpm rpm -i http://download.virtualbox.org/virtualbox/3.2.8/VirtualBox-3.2-3.2.8_64453_rhel5-1.i386.rpm error: Failed dependencies:     libGLU.so.1 is needed by VirtualBox-3.2-3.2.8_64453_rhel5-1.i386     libSDL-1.2.so.0 is needed by VirtualBox-3.2-3.2.8_64453_rhel5-1.i386     libXmu.so.6 is needed b........
  • mdadm: /dev/sda1 is too small: 0K - solution


    I was creating a RAID array and got this error: mdadm: /dev/sda1 is too small: 0K mdadm: create aborted Of course sda1 is not too small, both partitions sda1 and sdb1 are identical in size: Disk /dev/sda: 2000.3 GB, 2000398934016 bytes 255 heads, 63 sectors/track, 243201 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x00000000    Device Boot      Sta........
  • mdadm can you downgrade the superblock?


    Why would you want to downgrade the superblock?  Old mdadm verisons like mdadm 2.5.6 only use the 0.90 superblock/metadata and new versions use 1,1.0,1.1 and 1.2 superblocks by default. There are some annoying caveats with this, first of all the new superblocks (later than 0.90) CANNOT be read by GRUB, so you won't even be able to install GRUB.  Even worse, old versions of mdadm CANNOT automatically detect arrays even if they were created with a new version of mdadm with th........
  • Centos 5.5 RAID 1 boot issue


    I installed 5.5 with a 300GB RAID 1 partition (boot is also on this partition).  It booted up fine the first few times until after I used a Live CD and accessed the array, and it became named /dev/md127 for some reason. Now whenI boot into CentOS I get a kernel panic and different errors, once I got "invalid superblock", even though the array is fine (it didn't happen again, probably because I was sure to dismount and stop the mdadm array properly). Here's what........
  • Convert HDD/Hard Drive Partition(s) into non-RAID into RAID 1 using existing data without data loss and without reformatting.


    Before we start I take no responsibility for this, you should have a backup and if you make a mistake during this process you could wipe out all of your data.  So backup somewhere else before starting this as a precaution, or make sure it's data you could afford to lose. The RAID 1 Setup (Hardware Wise) I've already setup my 2 x 1TB (Seagate) drives with identical partitions, make sure your new hard drive (the empty one) is setup like your curr........
  • Picking an FTPD (vsftpd) Server in Linux Centos/Debian


    I decided on using yum to help me decide even though I normaly use proftpd I decided to see what else I could find. yum search ftp Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile  * rpmforge: ftp-stud.fht-esslingen.de  * base: mirrors.netdna.com  * updates: updates.interworx.info  * addons: yum.singlehop.com  * extras: mirrors.netdna.com rpmforge   ........
  • OpenVZ backup container to a single file while it's running using "vzdump"


    Proxmox has made this free utility to backup running OpenVZ containers.  It's a great program which is actually just a PERL script but gets the job done.  This program is not 100% required because all it really does is cp -a from your container's path as far as I know but it is still good to have uniformity to how you backup your containers. For RPM distros such as Centos/RHEL/Fedora etc.. download and install this: wget http://www.proxmox.com/cms_proxm........
  • Starting/Creating Services


    Starting/Creating Serviceshttp://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/configtuning-starting-services.html That might help........
  • MySQL Reserved Words


    MySQL Reserved Wordshttp://dev.mysql.com/doc/mysql/en/reserved-words.html You should familiarize yourself with these because you will have unexpected results if you use any of them. Eg. try creating a table with what you think is valid syntax like this: CREATE Table Order( .......); The word 'Order' is a reserved word and used to ORDER the results so you will get a syntax error from this one and you would think everything is........
  • Writing/Burning a data CD-R/DVD-R or DVD+RW in Unix/Linux


    There's a lot of outdated information and confusion for system administrator's out there. One annoying task for many an Administrator has been backing up data in Linux.  You don't need any GUI tools such as K3B or GnomeBaker.  Both are excellent tools but for veteran command line users working remotely, using the keyboard is a great and possibly automated way to save yourself pain and hassle. At a later date we'll cover how scripting can automatically backup certain........
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