/ - rtt - IT Resource

  • systemd management using systemctl and journalctl to check systemd logs


    systemd is like the service manager for your Centos and other modern Linux distributions (including Debian/Mint/Ubuntu) allows you to enable services, stop them, restart them, check their status and even reboot your system. The key commands or arguments you will use with systemctl are the following: Unit Commands:   list-units [PATTERN...]         List loaded units &nbs........
  • Linux Centos 7 HowTo Install Yarn


    https://yarnpkg.com/lang/en/docs/install/#centos-stable   curl --silent --location https://dl.yarnpkg.com/rpm/yarn.repo | tee /etc/yum.repos.d/yarn.repo If you need node.js: curl --silent --location https://rpm.nodesource.com/setup_6.x | bash - yum install nodejs yarn........
  • Linux input/output error invalid program cannot read data on some CD-Rs and DVD-Rs on ASUS BW-16D1HT


    I've never seen this before in all of my years.  I have some very old CDs and DVDs 12-15 years old that seem not to work in this BD-R/DVD-R/CD-R Asus drive. The discs are fine actually and ironically they even work fine on a normal LG USB based BD-R drive! Here are the errors in Linux: [2914936.884924] attempt to access beyond end of device [2914936.884927] loop1: rw=0, want=730424, limit=688384 [2914954.556873] attempt to........
  • How to change reserved blocks in Linux partition


    user@box:~$ sudo tune2fs -l /dev/md99 [sudo] password for user: tune2fs 1.42.9 (4-Feb-2014) Filesystem volume name:   <nuser> Last mounted on:          /mnt/md50 Filesystem UUID:          976a8655-2619-4587-878c-dab07f7b7652 Filesystem magic number:  0xEF53 Filesystem revision #:    1 (dynamic) Fi........
  • USB 3.0 External HDD Enclosure Seagate UAS problems - [sdd] tag#1 CDB: Write(16) 8a 00 00 00 00 01 70 04 08 68 00 00 00 08 00 00


      This is a 8TB Seagate external USB 3.0 device apparently newer kernels use a module called "UAS" instead of "USB Storage" which causes issues as a lot of devices are not properly supported in UAS mode by the kernel driver.  The solution some say is to disable UAS specifically for your USB device but I'd rather just disable UAS altogether.   Solution blacklist UAS: *do not do this it does not work and just causes your USB 3.0........
  • [warn] RSA server certificate is a CA certificate (BasicConstraints: CA == TRUE !?) - Apache Error Solution


    Does this mean? [warn] RSA server certificate is a CA certificate (BasicConstraints: CA == TRUE !?) Basically it means you created your SSL Certificate as a CA the wrong way, usually with this command: openssl req -new -x509 -nodes -days 1530 -out server.crt -keyout server.key   How can you fix it and do it properly? Step 1.) Make a new Private KeyCreate server pass key:........
  • mdadm frozen and doesn't realize array is dead/missing failed due to unplugged drives


    This was a surprising bug but I unplugged all drives for an array md127.  At first it was just 1 drive and mdadm seemed to notice this.  I unplugged the second drive taking the array offline but mdadm did not realize it was offline and still showed a non-existent disk as being part of it.  This created problems trying to unmount it or even to stop this array with mdadm freezing.  As for how to fix it I can only think of making sure you are not in a mounted path of........
  • OpenVZ how to enable FUSE in the container


    vzctl set 2 --devnodes fuse:rw --save Where "2" is the ctid........
  • 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........
  • Openvz Enable netadmin


    vzctl set $CTID --devnodes net/tun:rw --capability net_admin:on --save........
  • ssh session and port forward or reverse port matching or assocation howto


    Use netstat with the -anpe option.  The e option shows the inodes and I do not know if it will always work or if it was by fluke but I was dealing with dozens of SSH sessions and needed to know which session was related to which forward (the PIDs of the SSH and SSHD did not match etc...) Notice the "59560675" and "59560762" those are almost identical, if you find two sets that are nearly identical except for the last 3 digits they may match (in my ca........
  • Vbox/Virtualbox devices grayed out for non-root user solution


    <p>It is a permissions issue that is hard to fix.</p> <p><strong>All but one USB device is greyed out.</strong></p> <p>I am already a member of &quot;vboxusers&quot;</p> <ul> <li>I have already enabled and disabled USB support for the guest.</li> <li>I have already reinstalled the latest VBOx guest editions</li> <li>If running as root it all works fine</li> <li>Changing........
  • heatbeat ERROR: NV failure (msgfromsteam): [>>> ] ha_msg_add_nv_depth: line doesn't contain '='


    Apr 17 11:55:47 Cluster01 heartbeat: [1426]: WARN: ha_msg_add_nv_depth: line doesn't contain '=' Apr 17 11:55:47 Cluster01 heartbeat: [1426]: info: >>> Apr 17 11:55:47 Cluster01 heartbeat: [1426]: ERROR: NV failure (msgfromsteam): [>>> ] I have never been able to reproduce the above but it happened on heartbeat-3.04-2 when I took a node down for testing. One thing I believe caused it was by configuring ha.cf........
  • mkdir: cannot create directory 'test': Disk quota exceeded - Solution


    mkdir: cannot create directory 'test': Disk quota exceeded You are out of inodes usually: df -i Filesystem            Inodes   IUsed   IFree IUse% Mounted on /dev/simfs            200000  200000       0  100% / none      ........
  • xen how to resize an image properly


    The best way I could figure out is to use another guest of some sort to do this, while assigning the disk that needs to be resized to the same guest. So say we have /dev/xvda as the guests drive and we've booted it up. We also have /dev/xvdb (this is going to be the image/disk to be resized). In this case it's based on an ext3/4 image. Run e2fsck on it to ensure there are no filesystem errors. e2fsck /dev/xvdb........
  • Directadmin Enable SSL


    It's really silly how DA doesn't enable SSL by default but is otherwise a stable, fast and secure control panel. Here's a copy and paste way of enabling SSL for Directadmin in just a few seconds: *setup SSL openssl req -x509 -newkey rsa:1024 -keyout /usr/local/directadmin/conf/cakey.pem -out /usr/local/directadmin/conf/cacert.pem -days 9999 -nodes That creates the public certificate and private key pair in the location Directadmin expects to fi........
  • Xen how to mount disk images off-line and access data


    fdisk -lu VPS.img last_lba(): I don't know how to handle files with mode 81ed You must set cylinders. You can do this from the extra functions menu. Disk VPS.img: 0 MB, 0 bytes 255 heads, 63 sectors/track, 0 cylinders, total 0 sectors Units = sectors of 1 * 512 = 512 bytes      Device Boot      Start         End   ........
  • Openvz Container IP not working suddenly Solution


    This may not apply to everyone but here is what happened to me. One day my IP connectivity for one container went dead, I could ping the hostnode from it and the hostnode could ping it but there was no external routing.  I restarted the network service but it didn't help. I checked the routing table inside the VPS and the host and everything looked normal.  I added another different IP on the same subnet to the container and it worked.  Right away I st........
  • Yahoo Mail (email) DNS Server Out Of Date Problems


    I don't expect this to be solved soon but some of Yahoo's DNS servers are out of whack.  I changed the IPs of some nameservers of some domains and now most Yahoo users can't e-mail to those domains! As you can see below by the "No MX or A records for mychangedomain.com", now Yahoo's DNS/mailserver DNS cache is wrong.  You would think they would at least have cached the old incorrect records, but instead for some reason their DNS cache has no entry and doesn't seem........
  • Linux High IOWAIT updatedb can't be killed and crash with mdadm


    high IO wait   424 root      39  19  1900  848  552 D  0.0  0.0   0:00.91 updatedb root       424  0.0  0.0   1900   848 ?        DN   Mar11   0:00 /usr/bin/updatedb -f sysfs?rootfs?bdev?proc?cpuset?binfmt_misc?debugfs?sockfs?usbfs?pipefs?anon_inodefs?futexfs?tmpfs?inotifyfs?eventp........
  • Directadmin DA Install Guide


    yum -y install openssl* gcc-c++ gcc flex g++ make;wget http://www.directadmin.com/setup.sh;chmod +x ./setup.sh;./setup.sh #enable SSL /usr/bin/openssl req -x509 -newkey rsa:1024 -keyout /usr/local/directadmin/conf/cakey.pem -out /usr/local/directadmin/conf/cacert.pem -days 9999 -nodes chown diradmin:diradmin /usr/local/directadmin/conf/cakey.pem chmod 400 /usr/local/directadmin/conf/cakey.pem sed -i "s/SSL=0/SSL=1/g" /usr/local/dire........
  • Openvz Enable TUN/TAP OpenVPN


    Make sure the module "tun" is loaded on the host. vzctl set 2000 --devnodes net/tun:rw --save *Note what's below is what OpenVZ says you need (but I've never had to do it) vzctl exec 2000 mkdir -p /dev/net vzctl exec 2000 mknod /dev/net/tun c 10 200 vzctl exec 2000 chmod 600 /dev/net/tun On the container test the device: when Something is wrong:........
  • Dovecot Enable SSL/TLS with your certificate


    Dovecot enable SSL (by default it uses an old expired cert if you choose pop3s and imaps as protocols) =================== Create Cert & Key: openssl req -new -x509 -nodes -days 1530 -out server.crt -keyout server.key mkdir /etc/mailssl chmod 700 /etc/mailssl cp server.* /etc/mailssl Edit /etc/dovecot.conf ssl_cert_file = /etc/mailssl/server.crt s........
  • Postfix Enable SSL/TLS with your certificate


    Create Cert & Key: openssl req -new -x509 -nodes -days 1530 -out server.crt -keyout server.key mkdir /etc/mailssl chmod 700 /etc/mailssl cp server.* /etc/mailssl Postfix SSL config Edit /etc/postfix/main.cf: #SSL stuff smtpd_tls_cert_file = /etc/mailssl/server.crt smtpd_tls_key_file = /etc/mailssl/server.key To make smtps w........
  • Openvz Disk quota exceeded inode problem with free space


    Openvz problem, it is confusing because it's an inode issue and there is enough free space. cp: cannot create regular file `forums/memberlist.php': Disk quota exceeded /dev/simfs             60G   20G   41G  33% / none                  2.0G  4.0K  2.0G   1% /dev........
  • Ubuntu/Debian DRBD 8.0 Setup Guide


    I've only used it on Centos, so I thought I'd make a quick Debian guide: Install the DRBD Package apt-get install drbd8-utils Reading package lists... Done Building dependency tree       Reading state information... Done The following packages were automatically installed and are no longer required:   libswfdec-0.8-0 Use 'apt-get autoremove' to remove them. The following........
  • mdadm won't boot due to fsck error


    Nov 29 20:17:58 ubuntu kernel: [ 1157.180789] md: md1 stopped. Nov 29 20:17:58 ubuntu kernel: [ 1157.180829]  md0: unknown partition table filesystem not responding/reading properly with du or rsync (this needed an fsck). [ 2571.489217] EXT3-fs error (device md2): ext3_lookup: deleted inode referenced: 35923106 [ 2571.942299] EXT3-fs error (device md2): ext3_lookup: deleted inode referenced: 35923110 [ 2571.9568........
  • Initializing quota ... Error: Not enough parameters, diskinodes quota not set


    Initializing quota ... Error: Not enough parameters, diskinodes quota not set vzctl set $veid --diskinodes 90000:91000 --save   New versions of OpenVZ seem to have some strange diskinodes parameter which is required.........
  • DRBD WFConnection Problem/Solution


    This has stumped me  a few times because I keep forgetting that Centos 5.5 comes with a default iptables configuration that ends up blocking DRBD traffic, I tried all the normal things and couldn't understand why I couldn't make my normal DRBD config work.  So if you have WFConnection problems and have tried the normal "mailing list" fixes, check your firewall status first! Both Nodes Say the Following: version: 8.3.8 (api:88/prot........
  • Openvz Live Migration Error - Error: undump failed: Invalid argument Restoring failed: Error: iptables-restore exited with 2 Error: Most probably some iptables modules are not loaded Error: rst_restore_net: -22


    Adding IP address(es): 192.168.5.8 192.168.5.9 Setting CPU units: 1000 Error: undump failed: Invalid argument Restoring failed: Error: iptables-restore exited with 2 Error: Most probably some iptables modules are not loaded Error: rst_restore_net: -22 Container start failed Stopping container ... Container was stopped Container is unmounted Error:  Failed to undump VE Resuming... vzquota : (erro........
  • 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........
  • Linux EXT3 16GB-17GB maximum filesize issue solved/how to fix


    I have no idea why but mkfs.ext3 defaults to a patheticlly small blocksize of 1024 bytes/1KB (kilobyte).  That means the maximum filesize is ONLY 16GB!  With 2KB/2048 bytes you get a 256 GB maximum filesize, and with 4KB/4096 bytes you get 2TB! I finally noticed/paid attention to this after realizing that with rsync and scp that no file larger than 17GB could be transferred.  I then realized it must be a file size limit on the partition. Here is what tune2fs tol........
  • 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   ........
  • Create/Enable SSL Certificates for Apache on Linux/Unix Systems eg. Redhat,Centos,Debian


    Shortcut/Easiest Way To Create A Self-Signed Key: openssl req -new -x509 -nodes -days 1530 -out server.crt -keyout server.key Using the above, you instantly create a self-signed certificate valid for 1530 days and you can simply skip to step #5.) below. If You Need a Real SSL Certificate (eg. Equifax/Openssl) then you need to create a CSR request (you'll need to follow Steps 1.) and 2.) in order to create the CSR.  You then upload the CSR Certi........
  • GRUB "Error 2: Bad file or directory type" 0.97 won


    You can see the problem below, GRUB recognizes my hard drive and sees the partitions but cannot access them.  This is from the GRUB boot disc I'm using. What happened is that I had some power issues causing this system's power to be interrupted several times and basically an on/off on/off situation. The system won't boot, I just get a flashing cursor and no message or error from GRUB.  Obviously the problem is that my MBR seems corrupt or some other issue. My........
  • Configuring OCFS2 Clustered File System on Debian Based Linux including Ubuntu and Kubuntu


    There's a lot of information and guides on OCFS2 for RHEL and Centos Linux but the package setup and configuration is slightly different and this has thrown some people off. Installing OC2FS You should install the following packages to get started: apt-get install ocfs2-tools ocfs2console Configure OC2FS In RHEL/Centos the main configuration file is located in /etc/sysconfig/o2cb However in Debian based Linux it is located........
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