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.
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Recital provides a wide variety of connectivity solutions to external data sources. This article provides an overview.
After an extended period of intense software development, we are pleased to announce the release of Recital 10 which is a milestone in our development efforts.
The Recital 10 release notes can be found here.
- Recital
A powerful scripting language with an embedded database used for developing desktop database applications on Linux and Unix.
- Recital Server
A cross-platform SQL database and application server.
- Recital Web
A server-side scripting language with an embedded SQL database for creating web 2.0 web applications.
Recital provides the following additional benefits:
- Easy to Install and Deploy - Users can set up Recital in minutes enabling organizations to deliver new applications faster than other databases.
- Easy to Administer - Recital is a low administration database that eliminates the need for highly trained, skilled, and costly database administrators to maintain the database.
- High Performance - Superior database performance for the most demanding of OLTP applications. Additionally, Clustered Recital provides 99.999% availability.
- Embeddable Library - Recital Embedded Edition provides in-process data storage engine that delivers all the features of a traditional relational database but in a size which makes it ideally suited for ISVs/VARs who need a small footprint and easy to use toolkit.
- Platform Independence - Recital runs on Linux, Solaris, AIX, HP-UX, Windows, and Mac OS X giving organizations complete flexibility in delivering a solution on the platform of their choice.
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)
I am a fan of the previous incarnation of the PlugComputer so I was excited to see that Marvell have unveiled a new PlugComputer dubbed imaginatively "PlugComputer 3.0."
PlugComputer 3.0 Features:
Smaller sleeker design,
More powerful CPU - 2gz Armanda 300 CPU,
120GB 1.8-inch SATA hard drive,
Wifi,
Bluetooth,
10/100/1000 wired Ethernet,
USB 2.0.
512MB of RAM
512MB of Flash memory
I for one would like to see an additional Ethernet port added to increase application flexibility, for some applications where you are using clustered plugs or even for routing, having multiple Ethernet ports is a must.
Even without multiple ethernet ports, these low power consumption devices really could have a place in SME environments, replacing large cumbersome legacy hardware with compact Linux plug servers.
More information about the PlugComputer can be found here
SE Linux is a feature of the Linux kernel that provides mandatory access control. This policy based access control system grants far greater control over the resources on a machine than standard Linux access controls such as permissions.
Many modern Linux distributions are shipping with SELinux enabled by default, Fedora 14 and Rhel 6 both install with it enabled.
When you run Recital Web on a SELinux enabled machine and navigate to the default.rsp page you will see something similar to the screen shot below.
If you launch the SELinux troubleshooter you will see the following problem.
SELinux is blocking the apache server from accessing the Recital server running on port 8001.
To manage you SELinux policy you must have the policycoreutils package group installed. The policycoreutils contains the policy core utilities that are required for basic operation of a SELinux system.
If you wish to use a GUI tool, you must install the policycoreutils-gui package.
At the command prompt execute the following:
As root
$ yum install policycoreutils
$ semanage port -a -t http_port_t -p tcp 8001
$ service recital restart
$ service httpd restart
We use the semanage command here to allow the http server access to port 8001. Once you have completed the steps detailed above you can go and navigate back to the default.rsp page in your borwser, where you will find the permission denied message is now replaced by the default.rsp page.
SELinux does a great job of restricting services and daemons so rather than simply disabling it, why not work with it!
When it comes to security, every little bit helps...
// declare some simple procedures
proc display(cArg)
echo "display=" + cArg
endproc
proc show(cArg)
echo "show=" + cArg
endproc
// create an object based on an anonymous class
myobj = new object()
// add some properties
myobj["name"] = "barry"
myobj["company"] = "recital"
// now declare an anonymous method
myobj["mymethod"] = display
// call the method
myobj.mymethod("hello world") // displays "display=hello world"
// redeclare the method
myobj["mymethod"] = show
// call the method
myobj.mymethod("hello world") // displays "show=hello world"
Where this becomes particularly useful is when you have a procedure that calls anonymous methods in order to process data. This technique can be used to call anonymous procedures in your code.
proc processdata(oArg)
oArg.mymethod(oArg.name)
endproc
proc show(cArg)
echo "show=" + cArg
endproc
myobj = new object()
myobj["name"] = "barry"
myobj["mymethod"] = show
processdata(myobj) // displays "show=barry" $ lsof | grep db.exe | grep accounts db.exe 16897 john 6uw REG 253,0 20012 3413872 /usr/recital100/qa/accounts.dbf db.exe 16897 john 7u REG 253,0 4176 3413885 /usr/recital100/qa/accounts.dbxIf you want to check for locks you can use lslk, for example;
$ lslk | grep db.exe | grep accounts db.exe 16897 253,0 3413872 20012 w 0 0 0 12319 0 /usr/recital100/qa/accounts.dbfIf you don't have lslk installed you can install it with one of the updaters, for example on redhat linux:
$ yum update lslk