Server Administration

  • BIND/NAMED woes


    Feb 5 01:39:33 server named[19768]: zone myzone.com/IN: serial number (12331465) received from master 127.0.0.2#53 < ours (200901281) The above is taken from /var/log/messages This can be annoying, it can happen for a variety of reasons. What seems to be happening here is that the slave realizes the time on the slave is ahead of the master, so it therefore assumes it has the most up to date copy and won't actually transfer the zone. The solution is easy. Here's what you type on the slave: rndc retransfer myzone.com *Replace "myzone.com" with the actual name of the domain you want to transfer to the slave (of course the slave must already have the domain defined in /etc/named.conf. Remember that "myzone.com" is the domain name, even if you have a zone file called "myzone.com.db" you wouldn't type that or it won't work. The command above forces BIND to transfer the zone no matter what.
  • Apache Ignoring/Not processing .htaccess file


    I was getting very frustrated one day wondering why it appeared my .htaccess file was being ignored and not processed by Apache. No matter what I did it was obvious that Apache didn't care about my .htaccess file. Then I realized that the default settings must be in effect, which is that my vhost didn't explicitly allow me to override the default settings. This usually comes down to your vhost settings. Make sure you have an entry like this in your Apache vhost settings in order for .htaccess files to be processed, otherwise the default .htaccess settings in /etc/httpd/conf/httpd.conf are what take effect. Options FollowSymLinks AllowOverride All As you can see above, you just need an entry like this to fix the problem. Be sure that the path in the
  • MySQL Restoring And Dumping/Backing UP MySQL Data/Tables/Databases


    Backing MySQL Databases Backing Up/Dumping All Mysql Databases To A Single File mysqldump --all-databases -u admin -p > allmysqldatabases.sql The "-all-databases" clause is pretty obvious isn't it? It means that it will backup all databases. The "-u admin" means login using the user "admin", if you have another user such as root or a specific user that can access/dump all databases you can use that one. The ">allmysqldatabases.sql" part tells it to output all the database information to a file called "allmysqldatabases.sql" and don't forget the ">" as that is redirection and is what writes all the info to a file. Without redirecting the output, you'll see lines and lines of gibberish on your screen, because otherwise MySQL assumes you want to print all the output to the screen. This method is a quick and dirty way to migrate several databases at once. After that if you want to get fancy, you can gzip your database dump, this will protect against unknown data corruption and of course make the file transfer quicker since compressing with gzip reduces the size. For example the file was originally 279MB and gzip took it to 179MB. To gzip your backed up mysql databases just run this command (works on any file other than just .sql dumps of course): gzip allmysqldatabases.sql and it leaves you with "allmysqldatabases.sql.gz" in compressed gzip format. Backing Up A Single Mysql Database mysqldump --databases mysql -u admin -p > mysqlbackup.sql The "--databases" clause specifies you are going to backup one or more database as specified in the command. If you wanted databases "mysql" and "someothedb" you would use "--databases mysql someotherdb" Backing Up A Specific Table mysqldump -u user -p databasename tablename tablename > thetable.sql As you can see after specifying the db name you can specific as many tables you want. By default the tables will be populated with the data. If you just want the structure use this instead. mysqldump -d -u user -p databasename tablename tablename > thetable.sql The "-d" switch causes only the structure to be dumped. Restoring MySQL Databases What fun is backing up without being able to restore? Restoring can be a bit more tricky and there's a few different scenarios and options you have. I'll focus on the most common one, a new MySQL Server install with no previous data or tables. I'm assuming you've transferred your database backup "allmysqldatabases.sql.gz" To restore all your database(s) and information to MySQL just run this following command: mysql -u root < allmysqldatabases.sql Restoring a specific MySQL database/script backup to a specific database mysql -u $username --password="$password" --database="$dbname" < $sqlscript Issues/Problems/Complications with Restoring MySQLDatabases One issue I have is that despite backing up and restoring the database "mysql" I cannot authenticate successfully with my old login information. I don't know why because a query of the mysql table shows the usernames I am expecting to see. I'll have to research more on this point, but the good news is that all the other tables/databases and entries are there as expected. *UPDATE Iknew everything was there and that the "mysql" table was fully populated. All I had to do was restart mysql server (mysqld) and everything worked as normal with the old passwords and privileges Ioriginally had.
  • Linux Bash Shell Cannot/Can't View File That Starts With - Dash ?


    Iwas getting really annoyed with this, I used full quotes around the filename and vi, cat, less all thought I was trying to pass the dash in the filename as an argument. I didn't realize that all you have to do is just put a dash dash "--"in front. Here's an example:cat -- "-etc-glusterfs-glusterfsd.vol.log" Without the -- you get: cat: invalid option -- c Try `cat --help' for more information. Ihope this saves someone else some trouble. I never thought that a dash of anything could fix such an annoying problem :) I still think it's not preferable to have a filename which starts with a - but gusterfs thinks it is a smart thing for now.
  • Mysqld Solution - Can't init databases /usr/libexec/mysqld: Can't read dir of '/tmp/' (Errcode: 13) /usr/libexec/mysqld: Can't create/write to file '/tmp/ibyP1qUC' (Errcode: 13) 100215 7:02:24 InnoDB: Error: unable to create temporary file; errno


    100215 07:02:24 mysqld started /usr/libexec/mysqld: Can't read dir of '/tmp/' (Errcode: 13) /usr/libexec/mysqld: Can't create/write to file '/tmp/ibyP1qUC' (Errcode: 13) 100215 7:02:24 InnoDB: Error: unable to create temporary file; errno: 13 100215 7:02:24 [ERROR] Can't init databases 100215 7:02:24 [ERROR] Aborting 100215 7:02:24 [Note] /usr/libexec/mysqld: Shutdown complete 100215 07:02:24 mysqld ended One of my servers was rebooted for some reason and all sites and e-mail accounts were down because the database could not be connected. The first thing Ichecked was mysqld of course and it was not running. The above was revealed in /var/log/mysqld.log I was starting to panic and wondered if the server was compromised and I even checked /var/lib/mysql to make sure all the database data was still there. The solution for this MySQL Error is simple: chown root.root /tmp chmod 1777 /tmp And of course be sure that you start MySQL again.
  • 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 SSLCertificate (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 Certificate to your SSLProvider and they will e-mail you the .crt (SSL Certificate). Remember to keep your key from Step 1, you need the .key and .crt (from your SSL) provider to make use of your certificate. 1.) Create Your Private Key openssl genrsa -out ssl-private.key 2048 (note above I didn't include the -des3 switch as that makes you choose a passphrase for your key which we don't want). *Be sure not to lose this key file, especially if you are using the CSR request in Step 2.) to apply for a real SSL certificate Generating RSA private key, 2048 bit long modulus .............................................+++ ..................................................................................+++ e is 65537 (0x10001) Enter pass phrase for ssl-private.key: Verifying - Enter pass phrase for ssl-private.key: 2.) Create CSR Request (Certificate Signing Request) openssl req -new -key ssl-private.key -out ssl-request.csr Enter pass phrase for ssl-private.key: You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [GB]: State or Province Name (full name) [Berkshire]: Locality Name (eg, city) [Newbury]: Organization Name (eg, company) [My Company Ltd]: Organizational Unit Name (eg, section) []: Common Name (eg, your name or your server's hostname) []: Email Address []: Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []: An optional company name []: 3.) Remove Password/Passphrase From Private Key (otherwise Apache asks for the password each time you start it) mv ssl-private.key ssl-private.key-pass openssl rsa -in ssl-private.key-pass -out ssl-private.key Enter pass phrase for ssl-private.key-pass: writing RSA key 4.) Make Self Signed Certificate openssl x509 -req -days 730 -in ssl-request.csr -signkey ssl-private.key -out ssl-certificate.crt unable to load certificate 20243:error:0906D06C:PEM routines:PEM_read_bio:no start line:pem_lib.c:632:Expecting: TRUSTED CERTIFICATE *(don't forget the -req or you'll get the above error) 5.) Place CRT & KEY inside /etc/httpd/conf/httpd.conf or edit your VHOST conf cp ssl-private.key ssl.key/server.key cp ssl-certificate.crt ssl.crt/server.crt Here is what you should be inside the vhost (obviously be sure that you have the correct path and filenames): SSLEngine on SSLVerifyClient none SSLCertificateFile /etc/httpd/ssl-certs/server.crt SSLCertificateKeyFile /etc/httpdssl-certs/server.key *Remember to restart Apache or the new certificate won't be applied/take effect until you do.
  • Apache/Mod_SSL not serving the right/expected certificate?


    There is actually by default a "Default SSL" vhost that can mess things up for you and can cause surprising and unexpected results. Default Apache SSL Cert in /etc/httpd/conf.d/ssl.conf there is a default SSL Virtual Host which screws things up by offering itself instead of the SSL cert I specify in my own vhosts
  • Latest Articles

  • Why SMART is not smart at all and doesn't properly predict disk errors that cause a kernel panic or crash
  • scp: ambiguous target error and solution
  • VirtualBox How To Add iSCSI Storage using VBoxManage
  • iSCSI on Centos 7 Configuration and Setup Guide for Initiator and Target
  • Python and BeautifulSoup4's BS4's Decompose Method To Remove Unwanted Inner Tags
  • httpd AH00534: httpd: Configuration error: No MPM loaded. solution
  • bash script to remove modules from httpd.conf that are not actually installed
  • bash scripting how to create a function
  • Centos 7 PHP MySQL Not Working Solution
  • Bash How To Cut or Split Natively And Get The LAST Field
  • Bash Script How To Manipulate Text/Strings By Searchig and Replacing Natively
  • How Does Cisco CUCM (Cisco Unified Communication Manager) Work?
  • What DNS Options Does Active Directory Offer in Windows Server 2008,2012,2016 ?
  • syntax error, unexpected T_SL in PHP Solution
  • grep regular expression match number range between specific numbers
  • bash how to print out lines of text within a range from the first occurrence
  • bash script how to to check LAN computers for open ports
  • MySQL Using mytop Debug Source of High IO and Slow Performance
  • How To Mathematically Convert and Calculate Binary Value To Decimal Value
  • systemd management using systemctl and journalctl to check systemd logs