Blogger Digest

Linux Command To Confirm Bad Sector

2006-10-15T23:11:00.001+08:00

Hard disk being one of the vital components in computer system. Unfortunately, hard disk is also being one of the most high risk and sensitive components that is prone to failures, owed to the fact of mechanical subsystem attached!

The Linux command badblocks could be used to run bad sector burn-in test on a new or suspected faulty hard disk. Just get a low end PC or server installed with Linux OS, attach the target hard disk to the IDE or SCSI bus, and run the badblocks command on the target hard disk. For example,

badblocks -svw -t random -p 3 /dev/sdb

get badblocks to perform three rounds of destructive write of random data to the second SCSI hard disk.

Be careful! The option switch -w performs destructive write. Never use this option switch on a partition with filesystem. Instead, use -n to perform non-destructive read-write on a partition with filesystem!

Related information:

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Checklist To Tune DB2 Performance

2006-10-15T19:50:00.001+08:00

DBA suggests few of the recommended database performance tuning tips for IBM DB2 database engine that is running on Linux server.

Linux kernel parameters tuning that applicable to DB2 version 8.1 and 8.2.

Executing command sysctl -A to print out current kernel parameters setting. Some of the notable are
- kernel.sem (Semaphore setting)
  Recommended Value : 250 256000 32 1024
- kernel.msgmni (Maximum system-wide queues)
  Recommended Value : 1024
- kernel.msgmax (Maximum size of messages in byte)
  Recommended Value : 65536
- kernel.msgmnb (Default size of queue in byte)
  Recommended Value : 65536
In order to retain these changes of kernel parameters on every system reboot, add the updated kernel parameters setting to /etc/sysctl.conf system file to do the great job.
DB2 database configurable parameters tuning.

After connecting to database called my_test_db by executing db2 connect to my_test_db, running another DB2 command db2 autoconfigure apply none to get DB2 database engine calculate the best recommended value of DB2 database configurable parameters. Some of the notable are
- LOGPRIMARY / LOGFILSIZ
  Larger log buffer required for OLTP workloads with high transaction rate.
- CHNGPGS_THRESH
  For databases with heavy update transaction workloads, make sure there are enough clean pages in the buffer pool by setting the parameter value equal to or less than the best recommended value calculated by DB2 database engine.
- LOCKLIST
  The amount of storage that is allocated to the lock list. Increase this value if lock escalations causing performance concerns, that logged as warnings in the db2diag.log file.
- DBHEAP
  Database heap per database. Needs to be increased for larger buffer pools.
- NUM_IOCLEANERS
  Large buffer pools require a higher number of asynchronous page cleaners.
Alternate page cleaning algorithm tuning.

DB2 UDB ESE v8.2 introduces a new buffer pool page cleaning algorithm which is not turned on by default. It is necessary to test this new page cleaning algorithm with the database workload. To turn on this alternate page cleaning algorithm, executing DB2 command

db2set DB2_USE_ALTERNATE_PAGE_CLEANING=YES

Related information:

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Disable Linux Reboot On CTRL+ALT+DEL

2006-10-15T18:39:00.001+08:00

Don't ever press CTRL+ALT+DEL key combination in a Linux server!

Windows guys used to press CTRL+ALT+DEL key combination follow by ENTER key to immediately lock the server running on Windows 2000 or Windows XP and above when they leave the server.

What is the default behaviour when pressing CTRL+ALT+DEL key combination in a Linux machine? Well, the default action of Linux in responding to CTRL+ALT+DEL key combination is to reboot the Linux machine immediately! Just press it once, not twice as in Windows Me, and Linux will not be kind to ask confirmation before it really rebooting itself!

Anyway, this Linux default behaviour in responding to CTRL+ALT+DEL key combination pressed could be tweaked, indeed. Edit the /etc/inittab system file, look for the line containing ctrlaltdel keyword, and then either

Remark the line ca::ctrlaltdel:/sbin/shutdown -t3 -r now to disable Linux from responding to the CTRL+ALT+DEL key combination

or
Replace the /sbin/shutdown -t3 -r now with something else, such as

dialog --clear --title "Information" --msgbox "Don't press CTRL+ALT+DEL key combination in Linux machine.\n\nTo reboot server, use init 6 or init 0 to shutdown Linux." 10 40;clear

which use the dialog box command to alert users with a text-based GUI information dialog box.

Related information:

The dialog box command is not a standard program installed by most Linux distribution. Find the dialog package from respective Linux distribution and install it.
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Which Command Is Linux Refer

2006-10-15T17:12:00.001+08:00

Opss! Executing ls command at keith login account displaying directories in blue color, executable file in green color, and plain text file in white color, etc.

But, when executing the same simple ls command at root login account does not differentiate file type by color scheme. How come?

Users who are familiar with shell built-in command alias will know that it is the alias that wrap the ls command with --color=none option switch. At the command prompt, type

alias | grep ls

will able to tell the fact of this.

The which command is used to find out which command the Linux shell interpreter is referring to in the current login session. The simple form of which command, such as which ls will show the path of the ls command without telling the alias name of it. Well, tweak which command with its command option switch and wrap it with alias command, such as this

alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'

Execute the which ls again, will now able to show both the ls command path and the alias of it, as shown in the diagram.

Related information:

Use the alias command to shorten the long Linux command
Using the ls command by examples
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alias Shorten Long Linux Command

2006-10-15T01:27:00.001+08:00

Tired of typing Linux command because of long list of command option switches? Try to use the command alias to relieve tired of typing long Linux command then.

As the command name suggests, the Linux shell built-in command alias allows a user-defined command to represent

A system command with long arguments, such as

find . -type d -print

This find command used with a long option switches to list all directories that exists from the current directory downwards. The find command could be rather long if more find command option switches applied.

This long command line could be made simple with an alias, such as

alias dirfind='find . -type d -print'

that allows user to execute the short user-defined command dirfind instead of typing out that long command line.
A series of system commands, such as

tar -zcvpf bin.tgz bin; [ $? -eq 0 ] && echo DONE || echo FAIL

These system commands execute sequentially, aim to check the tarball archive creation status upon its completion. If success then echo DONE else echo FAIL.

Again, by using the alias command could make it shorter and simple enough, such as

alias chkbkp='tar -zcvpf bin.tgz bin; [ $? -eq 0 ] && echo DONE || echo FAIL'

where the user could execute chkbkp at command prompt and the Linux shell will expanding it to that commands series.

Related information:

It is not advisable to declare and use alias in shell scripts. It is better to use a variable or a function for the purpose. Anyway, if insist, it is technically possible to use alias in shell scripts by turning on shell scripts option shopt -s expand_aliases before declaring and using an alias inside the shell scripts, such as the sample in diagram below.

By default, the parent shell where a shell scripts executed will always spawn the scripts execution into a subshell, unless explicitly run the shell scripts in the current shell environment. Shell scripts that is running in subshell will not able to use aliases defined in parent shell environment!

To run a shell scripts in current shell environment instead of spawning into subshell, use one of these two syntax

source testscripts.sh
or
. testscripts.sh

In Linux system, there is a file named .bashrc in each home directory. Use this file to define aliases, which will make the defined aliases effective on each login.
The login profile .bash_profile could also be used to define aliases. In fact, it is the .bash_profile which execute the .bashrc while a user login.
To remove an alias, simply use the shell built-in command unalias, such as unalias chkbkp
To list all the aliases defined in the current login session, just type the command alias at the command prompt will do.
Which command is the Linux shell refers to
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Booting Thin Client Diskless Workstation

2006-10-14T23:29:00.001+08:00

Bootp, shorts for Bootstrap Protocol, is an UDP network protocol which is originally defined in RFC 951 to assign IP address for network clients. Bootp is well suitable to apply in diskless workstation, workstation without operating system installed, or simply called thin client.

Bootp is not DHCP! Although both of these two protocols sound similar at first thought, but they are technically different and could be co-exists in the same server or network segment.

Hospitality management system giant, Micros System Inc, makes good use of bootp in its high rank Point-Of-Sale system called Micros 8700 HMS.

When the diskless Micros PC Workstation power on, the bootp enabled network interface card will broadcast its MAC address to the network. When the bootp daemon running on the Micros host receives the broadcast packets, it will assign a valid IP address follow by transferring a DOS operating system image to the PC Workstation according to the MAC-IP-Image mapping maintained in the bootpd configuration file.

Once the image transferring (via tftp protocol) completed, the diskless PC Workstation starts to boot up with the OS image parking in memory segment that act as RAM-DISK. When the boot up completed, the Micros diskless PC workstation functions as if it is a normal desktop PC pre-installed with DOS OS.

Bootpd server and clients could be reside on different network segment by deploying bootp relay agent. To make thing simple or get it up and running right during initial roll out, put both bootpd server and client on the same network segment.

Checklist when thin client unable getting IP address:

Replace a known good unit of thin client to rule out possibilities of

Faulty boot ROM embedded in NIC that is bootp enabled
Faulty Ethernet patch cable
faulty network access point or LAN point

Bootp daemon is not running. In Linux/Unix, execute

ps -ef | grep bootpd
or
lsof -i | grep 67

to confirm bootp daemon is running and listening to legacy port number (as shown in /etc/services file)
Incorrect MAC address to IP address mapping maintained in /etc/bootptab bootpd configuration file
ARP cache conflict at bootpd server. Executing the command

arp -a

to list the bootpd server arp cache. Confirm that there is no ARP cache conflict. To delete the conflict, for example conflict on IP address 192.168.1.3, execute command

arp -d 192.168.1.3
Use cross-over patch cable or straight Ethernet cable and a hub to directly link up the bootpd server and client to form an simple isolate network. If it works in this simple network infrastructure, then get network experts sit in for assistant. There might be firewalls or routers that have blocked the UDP packets from reaching to bootpd server.

Related information:

Tftp protocol in brief

Host A sends an read request (RRQ) or write request (WRQ) packet to host B. The packet containing the filename and transfer mode.
Host B replies with an acknowledgement packet (ACK) to WRQ or directly with a DATA packet in case of RRQ. The reply also serves to inform host A of which port on host B the remaining packets should be sent to.
The source host sends numbered DATA packets to the destination host, all but the last containing a full-sized block of data. The destination host replies with numbered ACK packets for all DATA packets.
The final DATA packet must contain less than a full-sized block of data to signal that it is the last. If the size of the transferred file is an exact multiple of the block-size, the source sends a final DATA packet containing 0 bytes of data.

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Repair Corrupted Outlook PST OST File

2006-10-12T08:47:00.001+08:00

PST, known as Microsoft Outlook personal folder file or email archive file, used to archive emails out from the mail box at server side to a local storage or network drive.

OST, known as Microsoft Outlook offline folder file, allows user to work with Microsoft Exchange mail box in an offline mode. For example, emails composed, Contacts or Calendar changes, etc, will be storing in the offline folder. These changes made in offline folder will be automatically synchronize with Microsoft Exchange Server once hook up to the network - emails composed will be sending out immediately and Contacts or Calendar changes are updated to server side objects.

Both the Microsoft Outlook PST and OST files are believed using MSDE database engine.

MSDE is a light-weight freeware version of Microsoft SQL Server database engine that Microsoft offers to attract database users (especially MS Access users, developers, students, educators, etc) to develop database projects using Microsoft SQL Server. The latest release of MSDE is called SQL Server Express edition.

MSDE built with limitation of accessing up to 2GB worth of data only. The same limitation occurs in MS Outlook PST and OST file as well!

Watch the size of PST and OST file! If they getting fatty, trim them down quickly to save archives of email from hitting the 2GB limitation or a file corruption will happened soon! The best practice is to create multiple PST or OST files to categorize email archives. For those email with attachment, it is easily reaching the 2GB limitation. So, more PST or OST files are needed to archive such emails with attachment!

Office 2000 and higher with latest patches installed is nice enough to alert users with an error message and disallow users from adding or receiving new email item, so to safeguard PST or OST file to become oversize and corrupted. Earlier versions of MS Outlook does not display any error or warning messages and allow users to oversize the PST or OST file until corruption!

Microsoft offers a tool called PST2GB to recover a MS Outlook PST file that is corrupted after storing over 2GB worth of data. Microsoft alleged that PST2GB is not a tool that is 100% work at all time! If PST2GB does work, it does not recover all of the data (the truncated data is missing).

PST2GB merely create a truncated copy of the PST file to under 2GB. The copy that is left after the PST2GB completes does not have all the original data because the PST2GB forcibly cuts a user defined amount of data (below 2GB) from the PST file.

In brief,
Data or the emails archive after the truncation boundary will gone missing.
There must be enough disk space, 2GB free disk space if as maximum as possible of recovery desired.

Steps to recover corrupted PST file as per Microsoft KB296088 (applied to MS Outlook 97 to MS Outlook 2002)

Download the PST2GB from Microsoft Download Center
Extract the downloaded file 2gb152.exe to an empty folder for these five files - Msstdfmt.dll, Msvbvm60.dll, Pst2gb.exe, Readme.rtf, Readme.txt
Start the Pst2gb.exe program.
Click Browse to select the oversize PST file and then click Open.
Click Create, select the name and location of the truncated data file to be created, and then click Save.
Enter the amount of the data that intended to truncate in the PST file. There is no absolute ideal figure for this but for the best results is using 20 to 25MB, more or less. If that works, repeat the process and truncate the original oversize PST file by only 15MB. If that works, then try the process with 5MB. If 25MB does not work, repeat the process and truncate the original PST by 35MB. If the process does not work, increase the amount until the process is successful.
Run the Inbox Repair Tool scanpst.exe on the smaller PST file.
Open the repaired PST file in Microsoft Outlook.
(Recommended but optional) If the file opens, right-click the root folder of the PST, click Properties, and then click Compact Now to start the compression. For a file of this size, the compression may take approximately 4-8 hours.
If the file does not open, discard the truncated PST file, and repeat the process with the original PST file. Truncate more data than in the first attempt, and try the process again.

If the following error message arise when trying to run the PST2GB Utility

Run-time Error '713': Class not Registered. You need the following file to be installed on your machine. MSSTDFMT.DLL

To resolve this error, follow these steps:

Microsoft Windows 98, Microsoft Windows 98 SE, Microsoft Windows ME

Copy the MSstdfmt.dll file to the C:\Windows\System folder.
Open a command prompt, and then type the following command

REGSVR32 C:\Windows\System\MSSTDFMT.DLL

Microsoft Windows NT, Microsoft Windows 2000, and Microsoft Windows XP

Copy the MSstdfmt.dll to the C:\<windir>\System32 folder.
Open a command prompt and type the following command

REGSVR32 C:\<windir>\System32\MSSTDFMT.DLL

where <windir> is either the WINNT or the Windows directory.

Related information:

PST2GB from Microsoft official download site
Inbox Repair Tool for MS Outlook 2000 to MS Outlook 2003
Inbox Repair Tool for MS Outlook 97
Inbox Repair Tool for MS Outlook 98
OST Integrity Check Tool for Outlook 2000
Mailbox Recovery for Microsoft Exchange 2000 Server
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lsof Identify Resource Locked Process

2006-10-11T23:44:00.001+08:00

Samba server comes with a handy utility called smbstatus to report users who are holding the shared resources.

Utilities used to find out processes that are locking system resources are among the most wanted system utilities for experienced users and system administrators. The lsof being one of such excellent utility that used to identify process or user that is locking system resource such as file or network socket.

For example, a system administrator could use the lsof -i to easily understand how the IBM MQ server communicate over the TCP/IP network with IBM Informix server. The lsof output, as in the diagram below, shows that the Informix oninit is listening to a user defined mnemonic port name stp which the IBM MQ server communicate with. The /etc/services system files is usually used to map a numeric port number to a descriptive port name defined by user.

Execute lsof -i TCP to report all processes that are accessing the TCP sockets found on the system
Execute lsof -i tcp:8080 to find out what process is holding TCP port 8080.
Execute lsof without any command options to list system wide resources that are using by processes running in the system.
Execute lsof -p 456 to show all resources that are being held by process id 456
Some programs might running on the Linux system by more than one instance. In this case, type lsof -c ProgramName instead of lsof -p PID to get a broader scope of view. For example, lsof -c squid to find out what are the resources held by all squid processes running on the system.
Execute lsof -u keith to confirm resources that are being held by user id keith
Execute lsof /home/keith/secretfile to find out what are the processes that are locking the specify file /home/keith/secretfile

Related information:

Another utility called fuser has similar features as of lsof utility. Executing fuser -m /media/cdrom will report all process id that are holding the specify resource.

Each of the process id suffix with an ASCII character code which represent the resource access type. These resource access type codes are not standardize among various Linux distributions. To be safe and accurate, always consult the fuser man page to confirm the code definitions.

To check out what process ID is using TCP port 8080, execute the fuser as fuser -n tcp 8080 or fuser 8080/tcp
The native network related Linux command netstat is a good tool to find out what program or command is binding to a TCP and UDP port. For example, there are Bind, Djbdns, etc, used to bind with port 53 for DNS protocol. By executing netstat command as

netstat -tulap

will shows both the program and process id that bind to the network port. The diagram below shows the commands output of lsof vs netstat.

Both of the commands displaying pseudo port name instead of numeric port number, where the mapping of pseudo port name and numeric port number is defined in /etc/services file.

The netstat command, however, able to display numeric port and IP address with -n option switch. For example, rewrite the command as netstat -tulapn

Note! Both netstat -tulap and lsof -i MUST be executed with root user account privileges, else nothing as those in the diagram above will be seen.
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Repair Corrupted Windows Boot.ini

2006-10-10T23:27:00.001+08:00

Boot up to Windows Recovery Console and execute command bootcfg to repair corrupted or recreate missing Windows boot.ini file.

The bootcfg command able to scan hard disks for installation of Windows NT 4.0 and above and then add them to existing boot.ini file. The command also able to rebuild a new boot.ini file if one does not exist.

A brief of bootcfg command usage and syntax

bootcfg /add scans the computer for Windows systems installed (for example Windows 2000 and Windows XP in a dual boot setup), displays the results to choose and add it to the Boot menu.
bootcfg /rebuild iterates through all Windows installations found in the PC, allows user to specify which installations to rebuild the boot.ini file.
bootcfg /list reads the boot.ini file and displays the operating system identifier, the operating system load options, and the operating system location (path).

Related information:

The bootcfg command syntax and usages
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Sending Windows Console Message

2006-10-10T22:43:00.001+08:00

Windows Me or 9x comes with one handy network chatting program called Winpopup. Simple GUI allows user at one computer to chat over the network with counterparts sitting at another networked Windows.

However, there is not similar Winpopup replacement for Windows 2000 and above. There are two ways to send a message, better known as console message or Windows Alerts, to networked system running Windows 2000 and above.

Via the Computer Management window

Right-click on the My Computer icon on Desktop
Click on the Manage option from the pop up context menu
Click on the Action menu of Computer Management window
Goto All Tasks option
Click on the Send Console Message... option to call up Send Console Message window.

Via Command Prompt

Click on the Start button
Click on the Program menu
Click on the Accessories menu
Click on the Command Prompt application
At the Command Prompt window, type

net send 192.168.1.2 "testing messages"

to send a messages "testing messages" to PC with 192.168.1.2 IP address.

It is possible to replace IP address with DNS name or domain name to send console message to all workstations of the said domain.
Type net help send for more syntax and usage information.

Related information:

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Restart VNC Remotely

2006-10-10T20:26:00.001+08:00

Opsss! Can't VNC over to remote hosts!

Might need to restart the VNC server, but how?

Restart Windows-based (Windows 2000 and above) VNC server

Right-click the My Computer icon on Desktop
Click the Manage option from the pop up context menu
Click the Action menu of the Computer Management windows
Click the Connect to another computer... option
Type the IP address or DNS name of the target PC running the VNC server
Enter the login authentication info when prompt
After connect successfully, click the Services and Applications on the left panel.
Click the Services option
Search for VNC Server service on the right panel, right-click on it, and click Restart option to restart the VNC server.

Restart Linux-base VNC daemon

Telnet or ssh over to target host that running the VNC daemon
Type the command vncserver -kill:1 to kill the VNC daemon running on DISPLAY:1, for example.
Type vncserver :1 to bring up the VNC daemon running on DISPLAY:1 again.
To ensure VNC daemon startup listening for connection, type

netstat -ant | grep 5901

where 5901 is the legacy VNC daemon listening port of DISPLAY:1 in the previous step. If the port is open and listening means that VNC daemon is up and running successfully.

Related information:

Running VNC daemon on Linux
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MD5 Shell Scripts Find Duplicate Files

2006-10-10T13:34:00.001+08:00

The shell scripts wrap the default md5sum program found on most Linux system to prepare a report of unique and duplicate files in a given directory.

The lengthy source code could be shorten if removing the DupUniRpt function which merely used to prepare an easy to read report that showing both the filename and number of duplicate and unique files.

By removing the DupUniRpt function call and function coding, do remember to add the line

cat $FM5L

right after the DupUniRpt function call in the if-else statement. The $FM5L is a semi-raw report file that groups duplicate and unique files together.

The wDupUniRpt.sh contain the same source code of DupUniRpt function source code, which could be used to prepare that easy to read report based on the semi-raw report file. This shell scripts created merely for easy debugging purpose.

Both these shell scripts have been tested successfully with as much as possible scenarios. The source code might be able to further enhanced for efficiency or bugs fixing if any. Any suggestive comments are greatly appreciated.

Related information:

wmd5.sh to report both filename and number of duplicate and unique files in a given directory
wDupUniRpt.sh used to report redundant and unique records in an ASCII file of sorted records.
MD5 checksum used to find redundant files
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Install Recover Console To Boot Menu

2006-10-09T23:06:00.001+08:00

Recover Console is not install to local hard disk by default during Windows installation.

In order to access to Recovery Console, normally practice is to boot up the system from the appropriate Windows setup CD. If the system is running on Windows XP, use the Windows XP setup CD. Note that Recover Console only available in Windows 2000 and above.

Other than access the Windows Recovery Console from bootable Windows setup CD, it is possible to install the Windows Recovery Console to local hard disk and configure it to appear as one of the Windows boot up option.

Install Recovery Console to local hard disk and enable Recovery Console as part of the Windows boot up menu option:

Click on the Start button
Click on the Run menu
Type D:\i386\winnt32.exe /cmdcons by assuming D: drive is CD-ROM drive letter in which the Windows XP Setup CD is loaded.
Click OK button and then follow the instructions on the screen to complete the straight forward setup and restart the computer at the end of setup process.
After the Windows reboot, edit the file C:\boot.ini with notepad editor. Note that this file is hidden system file which is not "appear" in Windows Explorer by default, unless turning on the view hidden file options.
If view hidden file option is not turn on, turn it on by

Open My Computer
Click on the Tools menu
Click on the Folder Options
Click on the View tab
Click on the Hidden files and folders
Click to select Show hidden files and folders option button.
Click to clear Hide protected operating system files check box
click OK to complete the turning on view hidden file procedures.

At the bottom of the file, append this line

C:\cmdcons\bootsect.dat="Recovery Console" /cmdcons

Note that changing the description "Recovery Console" to whatever meaningful name is possible.
Save and exit the edited file. On the next system boot up, notice that there is one new boot option called Recovery Console in the Windows boot up menu.

Related information:

Tweaking Windows Recovery Console
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Using ls Command By Examples

2006-10-09T22:01:00.001+08:00

The ls command is a Linux command that is used to list directory contents. In fact, it is a standard shell command that exists in all Unix/Linux variants.

Using ls command by examples

To list all files in ascending order of file name detailed with file modification time

ls -la
To list all files in descending order of file creation time in full or customized date-time format

ls -lact --full-time
ls -lact --time-style="+%d %m %Y"
To list all files in descending order of file creation time

ls -lact
To list all files in descending order of file size in kilobytes

ls -laSh
To list only directories

ls -ap | grep /
or
ls -al | grep ^d

Alternatively, use the find command as

find . -type d -print
To list only directories initial with rpt filename

ls -al rpt* | grep :$
or
find . -type d -name "rpt*" -print

Definition of ls file listing command option switch

option switch l used to list files in long listing detailed format.
option switch a used to list all files including hidden files which filename prefix with a dot.
option switch lct used together to list file in descending order of file creation time.

option switch lc list file creation time and sorted by filename.

option switch lt list file in descending order of file modification time.
option switch h used to list files size information in kilobytes (KB).
option switch S used to list files in descending order of file size in byte.
option switch r used to reverse the default of descending listing order to ascending listing order.
option switch --full-time or --time-style used to display time-related info in full or customized format.

Notes! If the ls command colour scheme is not easy to read, turn it off by either:

On ad-hoc basis by adding option switch. For example

ls /etc --color=none

to list /etc directory contents without color scheme turning on. OR
On selective login session only. Use the alias command to save typing efforts. For example, execute the command

alias ls="ls --color=none"

will cause subsequent ls command executing as if it is supplied with --color=none option switch and automatically turn off the color scheme.
On each login session of individual login acount only. Copy the file /etc/DIR_COLORS to the user home directory as $HOME/.dir_colors and edit the variable COLOR to become COLOR=none to do the job.

From the next user login onwards, type the command set | grep COLOR will notice that the COLORS variable changed as specified in the $HOME/.dir_colors setting file. Typing the ls command as usual which will disable the file listing color scheme automatically.

To turn on the color scheme again, simply rewrite the line COLOR=none to COLOR=tty or COLOR=auto will do.

The file /etc/DIR_COLORS is used to control file listing color scheme globally, meaning that all users account will be affected.

Related information:

Creation time vs modification time at Linux file creation time vs Linux file modification time section of Using find command by examples article.
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Microsoft Freeware Visual Studio Express

2006-10-06T06:27:00.001+08:00

Yes! Effective 19 April 2006, all Visual Studio 2005 Express Editions are free permanently!

Microsoft Express Edition includes a wide range of Microsoft flagship development tools such as MS SQL Server 2005, Visual Basic 2005, Visual C# 2005, Visual C++ 2005, Visual J# 2005, Visual Web Developer 2005. As long as Express keyword attached, such as Visual Studio 2005 Express Editions, it is a genuine Microsoft freeware edition.

For those who familiar with MSDE, SQL Server Express is the replacement. Microsoft alleged that the name MSDE was confusing to customers and partners because many did not realize that it was associated with SQL Server. By changing the name from MSDE to SQL Server Express there will be less confusion among customers and partners.

Everyone could use the Expression edition at no cost for the purpose of testing, learning, and even compile and sell the development project. Before this, Microsoft freeware such as Visual Basic Learning edition couldn't compile development into executable.

Related information:

Product comparison of Visual Studio 2005
Visual Studio Express frequently asked questions
Price comparison of Visual Studio 2005 products
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File Command Guess Linux File Type

2006-10-03T21:09:00.001+08:00

By convention, Windows system using 3 alphanumeric characters to serve as file extension. File extension telling Windows OS how to deal with the file, what program to manipulate the file, and to Windows users easily recognize a common file type.

There is no such strong concept of file extension in Linux as well as UNIX world. Linux folks, however, do practice to use file extension for some file formats such as compression or archive file format. Windows users might easily get cheated by file extension trap in Linux.

For example, it is perfectly fine to rename a PKZIP compatible zip file called backup.zip to backup.tgz or whatever filename. Later, if the user simply executing tar -zxvf backup.tgz might either get errors or see nothing and thought the file is corrupted.

Wait! Before deleting the file which thought to be corrupted, use the file command to inspect the file type first.

Type file backup.tgz at the command prompt, it shows that backup.tgz is actually a PKZIP compatible zip file. So, user should executing unzip backup.tgz to extract the zip file or rename backup.tgz to backup.zip before executing the unzip command.

Related information:

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Understand And Configure Linux Printer System

2006-09-26T14:53:00.001+08:00

Starting Redhat 7.3, Redhat Linux support two type of printing system known. These two subsystem are known as LPRng and CUPS respectively.

LPRng printing system, Redhat default printer subsystem, provides printconf as printer manager utility to configure /etc/printcap configuration file, printer spooler, etc.

While at command prompt, executing printconf-tui (Redhat 7.3) or redhat-config-printer-tui (Redhat 8.0) to bring up command line version of LPRng printing manager.

For the graphical version, click on the Main Menu => System Settings => Printing or type redhat-config-printer or printconf-gui at a XTerm or Gnome terminal shell prompt to bring up the same GUI program.
CUPS, shorts for Common UNIX Printing System, is an Internet Printing Protocol-compliant system for UNIX and Linux. CUPS printer subsystem uses the printer manager utility called lpadmin to configure /etc/printcap configuration file, printer spooler, etc. If CUPS is not the default printer subsystem, launch the Printer System Switcher application by executing the command redhat-switch-printer and set CUPS as the new default printer subsystem.

To allow only a few selected users to use a printer called inkjet-graphic, execute the command lpadmin -p inkjet-graphic -u allow:keith,jazz,alice and these setting will be updated to /etc/cups/printers.conf configuration file.

Note! The printer manager utility, printconf or lpadmin, saves any printer configurations made to the /etc/printcap setting file. If there is a need to make any printer configurations outside the printer manager utility, add them to the /etc/printcap.local file. The /etc/printcap file will be deleted whenever the printer manager executing or a server reboot.

Steps to add new printer is almost the same among printer manager utilities. In brief, these are the key points to get it works:

Give a descriptive queue name to distinguish the new printer with other printers or network resources, such as keith_laser, boss_laser, tenfloor_inkjet, etc.
Choose the appropriate printer queue type, such as LOCAL queue type for local physical attached printer, JETDIRECT for jetdirect printer, etc.
If there is option to select the Printer Device, rescan the devices for the correct device, or create a custom device. This will be the /dev entry that represents the interface between the device driver and the printer itself. In most instances, the device will be named /dev/lp0.
Choose a Printer Driver by selecting one from the extensive list. Drivers marked with an asterisk (*) are recommended drivers. If to configure remote printer or printer that does not have a corresponding driver in the list, the safest choice would be Postscript Printer. For JetDirect printers, Raw Print Queue is recommended.

To enable local printer sharing for remote host:

In local host which the printer attached, edit the /etc/lpd.perms configuration file to add in one line that will read ACCEPT SERVICE=X REMOTEHOST=</etc/host.lpd and make sure it should added before the line containing REJECT SERVICE=X NOT SERVER.
In the local host as well, edit the /etc/host.lpd printer access control file add in the full qualify DNS host name or IP address, one record per line, of hosts that are allowed to share the printer attached.
At the remote host, add the network printer as adding local printer except one has to choose a Unix Printer queue type and type the print server hostname and port (usually 631).

Related information:

LinuxPrinting.org is a database of documents about printing, along with a database of nearly 1000 printers compatible with Linux printing facilities.
Linux printing how-to from the Linux Documentation Project.
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Redhat Enterprise Linux System File Permission

2006-09-25T22:19:00.001+08:00

Redhat Enterprise Linux device file permission could not be changed simply by using the chmod command. Instead, the device file permission is set by udev hotplug subsystem which is included in almost every 2.6 kernel based Linux distribution that is shipping.

The configuration file /etc/udev/permissions.d/50-udev.permissions defines the permission of each devices present in the Linux system. For example,

To change the raw devices file permission, search for the line that read as raw/*:root:disk:0660
To change tape drive file permission, search for the line that read as st*:root:disk:0660

The default permission defined is 0660. Simply change the 4 digits code as usual to an expected permission, say 0666 instead of 0660.

Related information:

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System And Network Monitoring Freeware

2006-09-25T11:55:00.001+08:00

Nagios is the answer!

It is licensed under the terms of the GNU General Public License Version 2 as published by the Free Software Foundation.

Nagios is a powerful system and network monitoring application. It monitors hosts and services specified, alerting administrators when threshold triggered, and when they recover to healthy state.

Nagios is only available in Linux or UNIX variants. Although, it could helps to monitor Windows servers as well via the Windows version of Nagios client.

Nagios features:

Monitors network services such as SMTP, POP3, HTTP, NNTP, PING, etc.
Monitors server resources such as processor load, disk usage, etc.
Simple plugin design that allows users to easily customize own service checks.
Parallelized service checks.
Ability to define network devices hierarchy using "parent" hosts, allowing detection of and distinction between network devices that are down and those that are unreachable.
Notifications to contacts of email, pager, or user-defined method, when service or host status change.
Ability to define event handlers to be run during service or host events for proactive problem resolution.
Automatic log file rotation.
Support for implementing redundant monitoring hosts.
Optional web interface for viewing current network status, notification and problem history, log file, etc.

Related information:

Nagios official site
Nagios 2.0 documentation
Nagios Plugin is the open project at Source Forge to create Nagios plugin
Nagios Exchange is the official repository for third party Nagios plugin
Nagios plugin development guidelines
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Internet Explorer Turns FTP Browser

2006-09-25T00:12:00.001+08:00

FTP is a legacy file transfer protocol that has been widely used since the day of networked computing.

Other than using the serious typing of command line FTP client, such as the standard FTP client offers by all Windows system, Internet Explorer able to serve as GUI FTP browser too!

Follow these simple steps to turn IE into a graphical FTP client:

Click the Tools menu from Internet Explorer,
Click on Internet Options,
Click the Advanced tab,
Check the check box labeled as "Enable Folder View For FTP Sites",
Check the check box labeled as "Use Passive FTP". Set this option only if the PC is behind a firewall.
Click OK button to complete the setting.
Now, IE is ready to serve as graphical FTP browser. For example, type ftp://keith@188.8.1.10 in the IE address bar and press ENTER to instruct IE connect to FTP server 188.8.1.10 using FTP user account keith. Enter the password when prompt.
Click OK and wait. After successful authentication, an interface similar to Windows Explorer shown. Copy files or folders as usual!

Related information:

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Tweaking Windows Recovery Console

2006-09-23T00:04:00.001+08:00

The Windows Recovery Console is designed to help system administrators recover Windows-based computer that fails to start up properly. It is available only in command prompt. Hence the name "Console" attached. It looks like the Windows 9x boot disk, but Windows Recovery Console is more powerful and features rich than the old Windows boot disk.

Basically, Windows Recovery Console allow system administrators to:

Copy, rename, replace, and access to operating system files and folders
Enable or disable Windows services for next system bootup
Repair the file system boot sector or the Master Boot Record (MBR)
Create and format partitions

By default setup, Windows Recovery Console with Administrator account logon allows access to only

the root folder
the %SystemRoot% folder and sub folders of the Windows installation
the Cmdcons folder
the removable media drives such as the CD-ROM drive or the DVD-ROM drive

Trying access to folders other than those listed above will rejected with an "Access Denied" error message. Besides that, Windows Recovery Console disallow copy files from local hard disk to removable storage such as floppy disk. However, Windows Recovery Console allow copy files from removable storage to local hard disk or copy files from one hard disk to another hard disk.

Although, limitations imposed on default setup that stated above could be resolved by

First, enable setting in Local Security Policy.
1. Click on Start button,
2. Click on Run menu,
3. Type gpedit.msc and click OK button,
4. Click on Computer Configuration, Windows Setting, Security Setting, Local Policies, Security Options,
5. Look for "Recovery Console: Allow floppy copy and access to all drives and all folders" policy on the right pane and double-click it,
6. Select Enabled,
7. Click OK
Note! As a security measures, it might be wise to double-click on "Recovery Console: Allow automatic administrative logon" policy too and disable it.
Second and last, boot up to Windows Recovery Console, logon with Administrator login account, and execute these two commands:
1. set AllowRemovableMedia = true
2. set AllowAllPaths = true
3. set AllowWildCards = true to allow wildcard support for some commands such as del.
4. set NoCopyPrompt = true to disable prompt when overwriting an existing file.

Related information:

Install Windows Recovery Console
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Shell Scripts Monitoring Disk Space Utilization

2006-09-22T23:31:00.001+08:00

Nothing special. Just a simple shell scripts, could be served as an introduction of Unix Shell scripts programming, written to check disk space utilization of Linux (applicable to Unix too) filesystems or partitions.

Note! Ignore the left most numeric digits which are not part of the Shell scripts coding. These are line number indicators, which could be turned on in Vi editor using the :set nu command code.

It might be useful to comment out line 14th and remove the hash key on line 15th, which disable echo alert to console and enable alerts emailed to mail box. Configure Linux scheduler via the crontab -e to run this shell scripts, perhaps once a day, and get system administrators alarmed of critical free disk space before the system comes to halt.

Related information:

ChkFreeSpace.sh shell scripts source code
Vi editor quick cheat sheet
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Restart Disabled Windows Services

2006-09-19T22:53:00.002+08:00

What could be done besides rebooting Windows server when a particular Windows service become unavailable to start, stop, pause, resume, or restart?

Restarting a Windows service, particular a poorly coded third party Windows service, may turns out to become unable to start, stop, pause, resume, or restart, after the service timeout and fail to startup successfully again. All these five common actions or tasks are dimmed and become unavailable. Restart the Windows server is not the only way, and might not advisable too, to resolve the problem.

Try this before deciding to reboot the Windows server:

Right-click on the Windows service,

Select property,

Set the Startup type to Disabled,

Click OK,

Set to Startup type again to either Manual or Automatic,

Click OK again,

Now, this particular Windows service might able to perform one of the five common actions again. Restart the Windows server if these do not work perfectly too.

Fine Tuning Nagios Performance

2006-09-19T09:31:00.002+08:00

These optimization tips are suggested by Nagios official documentation. It might be useful to fine tune Nagios for optimum performance and effective monitoring service.

Enabling aggregated status updates with the aggregate_status_updates option to greatly reduce the load on the monitoring host especially when monitoring a large number of services. The downside of this approach is getting delay notification on status change.

If standard status log is used instead of aggregated status updates, consider putting the directory where the status log is stored on a ramdisk. Ramdisk helps to speed thing up by saving a lot of interrupts and disk thrashing.

Use max_concurrent_checks option to restrict the number of maximum concurrently executing service checks. Nagios is overloaded if the extinfo CGI showing high latency values, say more than 10 seconds, for the majority of service checks.

The overhead needed to process the results of passive service checks is much lower than that of normal active checks. Passive service checks are only really useful if there are some external applications doing some type of monitoring.

Compiled plugin (C/C++) runs more efficient and faster than interpreted script (Perl, etc) plugins. If really want to use Perl plugins, consider compiling them into true executable using perlcc utility which is part of the standard Perl distribution or compiling Nagios with an embedded Perl interpreter.

In order to compile in the embedded Perl interpreter, set the --enable-embedded-perl option in the configuration script before compiling Nagios. In addition, use the --with-perlcache option to enable embedded interpreter caching the compiled Perl scripts for later reuse.

The check_ping plugin used to check host states will performs much faster if break up the checks. This is due to the fact that Nagios judges the status of a host after executing the plugin once.

Hence, it would be much faster to set the max_attempts value to 10 and only send out 1 ICMP packet each time, instead of specifying a max_attempts value of 1 in the host definition and having the check_ping plugin send 10 ICMP packets to the host.

However, the pitfalls of this arrangement will happens when the hosts are slow to respond may be assumed to be down. Another option would be to use a faster plugin check_fping as the host_check_command instead of check_ping.

Do not schedule regular checks of hosts unless absolutely necessary. Set the value to 0 for check_interval directive in the host definition to disable regular checks of a host. Use a longer check interval if really need to have regularly scheduled host checks.

Disable the use_aggressive_host_checking option to speed up host checks. The trade off is that host recoveries can be missed under certain circumstances.

Set the command_check_interval variable to -1 if running a lot of external commands, i.e passive checks in a distributed setup, will cause Nagios to check for external commands as often as possible. This is important because most systems have small pipe buffer sizes (4KB). If Nagios doesn't read the data from the pipe fast enough, applications that write to the external command file (the NSCA daemon) will block and wait until there is enough free space in the pipe to write their data.

System configuration / hardware setup directly affecting how the operating system (and Nagios application) performs. CPU and memory speed are obviously factors that affect system performance, but disk access is biggest bottleneck. Don't store plugins, status log, etc on slow storage medium such as old IDE drives or NFS mounts. Always opt to use UltraSCSI drives or fast IDE drives whenever possible.

Note! Many Linux installations do not attempt to optimize IDE disk access. Use hdparam to change the IDE hard disk access parameters to gain speedy features of the new IDE drives.

Tweaking Windows Server LargeSystemCache

2006-09-17T22:16:00.002+08:00

LargeSystemCache determines whether Windows 2000 Server should maintains a standard size or a large size file system cache, and influences how often the system writes changed pages back to hard disk.

Increasing the size of the file system cache generally improves server performance, but it reduces physical memory space available to applications and services. In addition, writing system data less frequently minimizes use of the kernel disk subsystem, but the changed pages occupy memory that might otherwise be used by applications.

LargeSystemCache is DWORD registry data type that could be located at registry path

HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management

Setting LargeSystemCache to 1 (system default)

Establishes a large system cache working set that can expand to physical memory, minus 4 MB, if needed. The system allows changed pages to remain in physical memory until the number of available pages drops to approximately 250. This setting is recommended for most computers running Windows 2000 Server as file server on large networks.

Setting LargeSystemCache to 0

Establishes a standard size file system cache of approximately 8 MB. The system allows changed pages to remain in physical memory until the number of available pages drops to approximately 1,000. This setting is recommended for servers running applications that do their own memory caching, such as Microsoft SQL Server, and for applications that perform best with ample memory, such as Internet Information Services web server.

Other than access to registry via regedit.exe and edit directly, alternative method to tweak LargeSystemCache is by

accessing to the Server Optimization tab in Network And Dial-up Connections,
right-click My Network Places,
click Properties,
right-click Local Area Connection,
click Properties,
click File And Printer Sharing For Microsoft Networks,
and then click the Properties button,
to set the LargeSystemCache to 0, select the Maximize Data Throughput For Network Applications option,
to set the LargeSystemCache to 1, select Maximize Data Throughput For File Sharing.

The default setup of Windows 2000 Server initialize LargeSystemCache to 1 which is ideal when running as file server. However, setting LargeSystemCache to 1 can degrade service performance. As such, it is not appropriate when running as application servers such as Web server, SQL server, Exchange server. In this case, reset LargeSystemCache to 0 by selecting the Maximize Data Throughput For Network Applications option in Network And Dial-up Connections.