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STRERROR()

Syntax

STRERROR( [ <expN> ] )

Description

The STRERROR() function returns a string describing the last operating system error message. If the optional error number is specified then the related operating system error message will be returned.

Example

mqdes=mqcreate("/myqueue", 2)
 if (mqdes < 0)
     messagebox(strerror()+",errno="+alltrim(str(error())))
    return
 endif
 rc = mqsend(mqdes, "Test message")
 if (rc < 0)
     messagebox(strerror()+",errno="+alltrim(str(error())))
    return
 endif
 mqclose(mqdes)

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If you have software packages which you wish to share with others or simply between your own personal machines, a neat and easy solution is to create your own YUM repository and provide your .repo file for download.

YUM is by far the easiest method of installing software on Red hat, Centos and Fedora. Not only does it mean you don't need to trawl the web looking for somewhere to download the packages, YUM does a great job of satisfying any package dependencies. As long as the required packages are available in the enabled repositories on your system, YUM will go out and get everything you need.

To create your own YUM repository, you will need to install the yum-utils and createrepo packages:

yum install yum-utils createrepo

yum-utils contains the tools you will need to manage your soon to be created repository, and createrepo is used to create the xml based rpm metadata you will require for your repository.

Once you have installed these required tools, create a directory in your chosen web server's document root e.g:

mkdir -p /var/www/html/repo/recital/updates

Copy the rpm's you wish to host into this newly created directory.

The next step is to create the xml based rpm metadata. To create this use the createrepo program we installed earlier.

At the shell type the following command:

createrepo -v -s md5 /var/www/html/repo/recital/updates


This will create the required metadata in the repodata directory of your /var/www/html/repo/recital/updates directory.

root@test repodata]# ls -l
rwotal 44
-rw-r--r-- 1 root root 28996 Jan 13 21:42 filelists.xml.gz
-rw-r--r-- 1 root root   284 Jan 13 21:42 other.xml.gz
-rw-r--r-- 1 root root  1082 Jan 13 21:42 primary.xml.gz
-rw-r--r-- 1 root root   951 Jan 13 21:42 repomd.xml

To do a final consistency check on your repository run the following command:

verifytree /var/www/html/repo/recital/updates

We now have a fully functioning YUM repository for our hosted rpm packages.
The next process is to create a .repo file in the client systems /etc/yum.repos.d directory.

Navigate to the /etc/yum.repos.d directory on your system as root.

Using your preferred text editor to create the .repo file. In this example I will call it recital.repo.
Now paste in the following lines:

[Recital]
name=Recital Update Server
baseurl=http://ftp.recitalsoftware.com/repo/recital/updates
enabled=1
gpgcheck=1

Once that is saved, at the shell prompt on the same machine (YUM client system).

$ yum repolist
Loaded plugins: presto, refresh-packagekit
repo id                  repo name                                 status
Recital                  Recital Update Server                     enabled:      1
adobe-linux-i386         Adobe Systems Incorporated                enabled:     17
fedora                   Fedora 12 - i386                          enabled: 15,366

As you can see the Recital repo is now being picked up and we have access to all the packages it is hosting.

See how easy that was!

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This website runs in a  virtual machine under vmware server. It is clustered between two servers using heartbeat and DRBD.
 
When VMware server starts up a virtual machine it generates a uuid (unique id) based on the machine it is running on and stores this in the .vmx file.
 
When heartbeat switches from slave to master, it will start VMware server (which is setup as a resource in the haresources file).
 
Virtual machines that you want started automatically when you start VMware server will not start because the uuid changes between the master and backup systems. To get around this problem always do the following:
  • edit the .vmx file and add the following line

    uuid.action = "keep"
If this is not done then everytime you try to run the virtual machine on the backup system in your cluster, VMware server will complain that the virtual machine has been copied or moved and it will not start it.
  • set the virtual machine to power off when vmware is stopped. Do not set this to "suspend" or it will not restart on the backup machine.
This will allow the virtual machine to start properly on the backup machine.
 
 
 
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Recital is a dynamic programming language particularly suited to the development of database applications. While Recital still supports standard procedural programming, new extensions to the language give you the power and flexibility of object-oriented programming. Object-oriented design and object-oriented programming represent a change in focus from standard procedural programming. This short primer will give you a good understanding of how to program object-oriented Recital.
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If you have 4 GB or more RAM use the Linux kernel compiled for PAE capable machines. Your machine may not show up total 4GB ram. All you have to do is install PAE kernel package.

This package includes a version of the Linux kernel with support for up to 64GB of high memory. It requires a CPU with Physical Address Extensions (PAE).

The non-PAE kernel can only address up to 4GB of memory. Install the kernel-PAE package if your machine has more than 4GB of memory (>=4GB).

# yum install kernel-PAE

If you want to know how much memory centos is using type this in a terminal:

# cat /proc/meminfo
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Recital 10 enhances the APPEND FROM command. The enhancement was added to the following syntax ;
APPEND FROM  <table-name> 
Before when appending into a shared Recital table each new row was locked along with the table header, then unlocked after it was inserted. This operation has now been enhanced to lock the table once, complete inserting all the rows from the table and then unlock the table. The performance of this operation has been increased by using this method. All the database and table constraints are still enforced.
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A good article describing the configuration of samba for file/record locking can be found here.

Basically you must add these directives to the smb.conf file:

[data] 
oplocks = False 
level2 oplocks = False

The default oplock type is Level1. Level2 oplocks are enabled on a per-share basis in the smb.conf file. Alternately, you could disable oplocks on a per-file basis within the share: 

veto oplock files = /*.dbf/*.DBF/*.ndx/*.NDX/*.dbx/*.DBX/*.dbt/*.DBT/

You can further tune samba by following this guide.

If you specify the Common Internet File System (CIFS) when you mount the samba share then you must specify the following options
mount -t cifs {mount-point} -o username=name,pass=pass,directio
The directio option is used to not do inode data caching on files opened on this mount. This precludes mmaping files on this mount. In some cases with fast networks and little or no caching benefits on the client (e.g. when the application is doing large sequential reads bigger than page size without rereading the same data) this can provide better performance than the default behavior which caches reads (readahead) and writes (writebehind) through the local Linux client pagecache if oplock (caching token) is granted and held. Note that direct allows write operations larger than page size to be sent to the server.

If you get the following error when trying to mount the {mount-point}
Apr 22 16:57:39 bailey kernel: Status code returned 0xc000006d NT_STATUS_LOGON_FAILURE
Apr 22 16:57:39 bailey kernel:  CIFS VFS: Send error in SessSetup = -13
Apr 22 16:57:39 bailey kernel:  CIFS VFS: cifs_mount failed w/return code = -13
The you need to create the Samba user specified on the mount command
smbpasswd -a username
FYI - Make sure you umount all the Samba {mount-point(s)} before shutting down Samba.
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In this article Barry Mavin explains step by step how to setup a Linux HA (High Availability) cluster for the running of Recital applications on Redhat/Centos 5.3 although the general configuration should work for other linux versions with a few minor changes.

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After installing nomachine, if you get an error connecting whereby nomachine errors out after  "Negotiating link parameters"
 

When installing nomachine on redhat 5.3 64-bit be sure to:

  1. Make sure you have installed the 64-bit packages as the 32-bit ones will not work.
  2. add the hostname to /etc/hosts
  3. Check "Disable encryption of all traffic" (in configuration / advanced tab)
On Centos 32-bit:
  1. add the hostname to /etc/hosts
  2. make sure the host IP is not specified as 127.0.0.1 line
  3. Uncheck "Disable encryption of all traffic" (in configuration / advanced tab)
 
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If you are running your Redhat/Centos or Fedora machine in an enterprise environment you may be sitting behind a network proxy server like squid.

If you try and update or install software it will fail with timeouts or errors contacting the repository mirrors.

To configure YUM to work with your proxy server you need to add the following line to your /etc/yum.conf file.

Anonymous proxy configuration:
proxy=http://yourproxyip:port/

If your proxy server requires authentication add the following lines to your /etc/yum.conf file instead.

proxy=http://yourproxyip:port/
proxy_username=youruser
proxy_password=yourpassword

 You will be able to update and install software now, give it a go!

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