παραδείγματα χρήσης συμβόλων σε command line
Symbol - Function - Example
>
Sends output to a named file. If file does not exist, it creates one. Overwrites existing file
command > somefile
>>
Appends output to contents of a named file or creates a file if none exists
command >> somefile
¦
Sends ("pipes") the output of command1 to the input of command2
command1 ¦ command2
&
Used to combine two commands. Executes command1 and then command2
command1 & command2
&&
A conditional combination. Executes command2 if command1 completes successfully
command1 && command2
¦¦
Command2 executes only if command1 does not complete successfully.
command1 ¦¦ command2
@
Used in batch files at the beginning of a line to turn off the display of commands
@echo off
Thursday, December 17, 2009
Monday, December 14, 2009
Cisco Product Quick Reference Guide
Στον παρακάτω σύνδεσμο θα βρείτε τον κατάλογο των προϊόντων της Cisco σε μορφή pdf. Είναι εξαιρετικά χρήσιμος μιας και εκεί θα βρείτε το σύνολο των βασικών χαρακτηριστικών όλων των συσκευών της, σε ένα και μόνο pdf. Πολλές φορές το επίσημο site της εταιρείας είναι λίγο χαοτικό και ειδικότερα η αναζήτηση προϊόντων.
Wednesday, December 9, 2009
έλεγχος λειτουργίας μιας υπηρεσίας με telnet
telnet to a specific port
Telnet, by default, uses port 23. Ports are specific channels for network services and clients to use so that you can have more than one connection at once. Eg telnet works on port 23, ftp works on port 21, web(http) works on port 80 etc. Think of them as numbered doors into the same house. There is nothing to stop you using telnet (or some other services) on another port eg telnet into a web server by using:
telnet www.somewhere.com 80 or www.somewhere.com:80
While this may not be very useful unless you know how to run a specific protocol by hand (some people use this to check their mail on pop servers from very bare terminals) it is a quick way of checking that a certain service is running on a remote machine. If you can't telnet in on the specific port number then there's a good bet it isn't running.
A list of services and the ports they run on are contained in /etc/services. (σε linux)
Some services, even generic ones, may be run on different port numbers on certain machines for reasons of security or convenience and knowing about port numbers is helpful in this instance.
Telnet, by default, uses port 23. Ports are specific channels for network services and clients to use so that you can have more than one connection at once. Eg telnet works on port 23, ftp works on port 21, web(http) works on port 80 etc. Think of them as numbered doors into the same house. There is nothing to stop you using telnet (or some other services) on another port eg telnet into a web server by using:
telnet www.somewhere.com 80 or www.somewhere.com:80
While this may not be very useful unless you know how to run a specific protocol by hand (some people use this to check their mail on pop servers from very bare terminals) it is a quick way of checking that a certain service is running on a remote machine. If you can't telnet in on the specific port number then there's a good bet it isn't running.
A list of services and the ports they run on are contained in /etc/services. (σε linux)
Some services, even generic ones, may be run on different port numbers on certain machines for reasons of security or convenience and knowing about port numbers is helpful in this instance.
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