Occasionally as a Linux administrator you will be in the situation where working on a remote server and you are left with no option but to force a reboot the system. This may be for a number of reasons, but where I have found it most frequent is when working on Linux clusters in a remote location.

When the "reboot" or "shutdown" commands are executed daemons are gracefully stopped and storage volumes unmounted.
This is usually accomplished via scripts in the /etc/init.d directory which will wait for each daemon to shut down gracefully before proceeding on to the next one. This is where a situation can develop where your Linux server fails to shutdown cleanly leaving you unable to administer the system until it is inspected locally. This is obviously not ideal so the answer is to force a reboot on the system where you can guarantee that the system will power cycle and come back up. The method will not unmount file systems nor sync delayed disk writes, so use this at your own discretion.

To force the kernel to reboot the system we will be making use of the magic SysRq key.

The magic_SysRq_key provides a means to send low level instructions directly to the kernel via the /proc virtual file system.

To enable the use of  the magic SysRq option type the following at the command prompt:

    echo 1 > /proc/sys/kernel/sysrq

Then to reboot the machine simply enter the following:

    echo b > /proc/sysrq-trigger

Voilà! Your system will instantly reboot.
{linkr:related;keywords:linux;limit:5;title:Related Articles}
{linkr:bookmarks;size:small;text:nn;separator:%20;badges:2,1,18,13,19,15,17,12}

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!

In this article Barry Mavin, CEO and Chief Software Architect for Recital, details Working with Stored Procedures in the Recital Database Server.

Overview

Stored procedures and user-defined functions are collections of SQL statements and optional control-of-flow statements written in the Recital 4GL (compatible with VFP) stored under a name and saved in a Database. Both stored procedures and user-defined functions are just-in-time compiled by the Recital database engine. Using the Database Administrator in Recital Enterprise Studio, you can easily create, view, modify, and test Stored Procedures, Triggers, and user-defined functions

Creating and Editing Stored Procedures

To create a new Stored Procedure,  right-click the Procedures node in the Databases tree of the Project Explorer and choose Create. To modify an existing stored procedure select the Stored Procedure in the Databases Tree in the Project Explorer by double-clicking on it or selecting Modify from the context menu . By convertion we recommend that you name your Stored Procedures beginning with "sp_xxx_", user-defined functions with "f_xxx_", and Triggers with "dt_xxx_", where xxx is the name of the table that they are associated with.

Testing the Procedure

To test run the Stored Procedure, select the Stored Procedure in the Databases Tree in the Project Explorer by double-clicking on it. Once the Database Administrator is displayed, click the Run button to run the procedure.

Getting return values

Example Stored Procedure called "sp_myproc":

parameter arg1, arg2
return arg1 + arg2

Example calling the Stored Procedure from C# .NET:

////////////////////////////////////////////////////////////////////////
// include the references below
using System.Data;
using Recital.Data;

////////////////////////////////////////////////////////////////////////
// sample code to call a Stored Procedure that adds to numeric values together
public int CallStoredProcedure()
{
	RecitalConnection conn = new 
		RecitalConnection("Data Source=localhost;Database=southwind;uid=?;pwd=?");
	RecitalCommand cmd = new RecitalCommand();
	cmd.Connection = conn;
	cmd.CommandText = "sp_myproc(@arg1, @arg2)";
	cmd.CommandType = CommandType.StoredProcedure;
	cmd.Parameters["@arg1"].Value = 10;
	cmd.Parameters["@arg2"].Value = 20;
	conn.Open();
	cmd.ExecuteNonQuery();
	int result = (int)(cmd.Parameters["retvalue"].Value);    // get the return value from the sp
	conn.Close();
	return result;
	}

Writing Stored Procedures that return a Resultset

If you want to write a Stored Procedure that returns a ResultSet, you use the SETRESULTSET() function of the 4GL. Using the Universal .NET Data Provider, you can then execute the 4GL Stored Procedure and return the ResultSet to the client application for processing. ResultSets that are returned from Stored Procedures are read-only.

Example Stored Procedure called "sp_myproc":

parameter query
select * from customers &query into cursor "mydata"
return setresultset("mydata")

Example calling the Stored Procedure from C# .NET:

////////////////////////////////////////////////////////////////////////
// include the references below
using System.Data;
using Recital.Data;

////////////////////////////////////////////////////////////////////////
// sample code to call a stored procedure that returns a ResultSet
public void CallStoredProcedure()
{
	RecitalConnection conn = new 
		RecitalConnection("Data Source=localhost;Database=southwind;uid=?;pwd=?");
	RecitalCommand cmd = new RecitalCommand();
	cmd.Connection = conn;
	cmd.CommandText = "sp_myproc(@query)";
	cmd.CommandType = CommandType.StoredProcedure;
	cmd.Parameters["@query"].Value = "where not deleted()";
	conn.Open();
	RecitalDataReader dreader = cmd.ExecuteReader();
	int sqlcnt = (int)(cmd.Parameters["sqlcnt"].Value);    // returns number of affected rows
	while (dreader.Read())
	{
		// read and process the data
	}
	dreader.Close();
	conn.Close();
}