Here’s a simple command that setups a local port tunneling via SSH and a reverse SSH Port Tunneling at the same time.
screen -dm autossh -p  [111.222.333.444] [-L 5555:localhost:6666] [-R 7777:localhost:22]
Put this is your rc.local file to run this on startup.
- screen -dm creates a detached mode session other than your current one so you can have the command running after you exit the terminal
- autossh is like SSH binary but auto reconnects if ever your connection gets terminated.
- 22 is the SSH port, change this if you modified your server to listen on another port or your firewall does port forwarding
- 111.222.333.444 is your target server address
- -L 5555 is the local port number to use to forward your connection
- localhost no explanation needed
- 6666 the port on the other end to forward to
- -R 7777 the port to use on the other side to connect to your home server ( your source )
- localhost no explanation needed
- 22 ssh port used, change this if you are listening on another port
So, if you want to connect to your source server ( home server ), all you do is connect to localhost via the port that was opened to do reverse SSH.
I have a linux Ubuntu server and a dynamic IP for the DSL connection. The office needs web filtering and getting a static IP will just add cost to the now tight budget. Looking around there is actually a way to update OpenDNS IP address under linux. Below are what is needed to be installed and configured.
- Any latest Ubuntu server ( I’m using Ubuntu 10.10 Server )
- ddclient installed (use “aptitude install ddclient”)
- net connection, I have set up my linux server as a firewall/gateway
After installing ddclient, go to /etc and edit ddclient.conf, below is the format that I used, modify it to suite your configuration.
<openDNS_network_label_here> #this can be found under settings, just the label, nothing else should be added here
Save the new configuration file and restart the client
Also make sure that the network that your going to update the IP address has set its Dynamic IP Update option enabled. This can be found under the advance setting of the network.
I’m currently playing around with Java Native Interfaces(JNI) and I must say its been too long since I programmed in Java. Its good to be back! Anyway, lets hop to the main topic…
I was following the tutorial from Sun in creating my first JNI and calling my compiled C++ library, I was stuck in the last part where this error popped out whenever I tried to invoke
the error was…
java.lang.UnsatisfiedLinkError: no HelloWorld in java.library.path
at HelloWorld.<clinit>(HelloWorld.java:<line number>)
Could not find the main class: HelloWorld. Program will exit.
one way of fixing this is to include the current location of your newly compiled shared library (ex. HelloWorld.so). I’m using Ubuntu linux,so to include the current folder where your “.so” file is located, invoke…
or you can also do …
I had a problem in using a string-comma-separated-value returned from a query in an “IN” statement. I used the IDs from one table, concat them into a comma separated value and insert them into another table. Baaaad idea… Now when I query that value, I can’t use it directly into an “IN” statement to retrieve their real values since its a string being returned from the query, the “IN” statement will not compare all the values inside as a set, but it will compare it as a string.
SELECT value FROM my_table WHERE my_id IN (‘1, 2, 3’) is NOT equivalent to SELECT value FROM my_table WHERE my_id IN (‘1’, ‘2’, ‘3’)
So, if you have a table containing values 1 to 3, the first query will return only 1 while the second query will return all values; 1, 2 and 3.
I Googled around and found out that MySQL does not have a native equivalent of PHP’s explode() function. Crap… I had to do it the hard war and create a MySQL stored function to ‘explode’ the values from its delimiter, query the right value from the other table using the exploded IDs, concat them back together and return them as a string.
Below is the function I was able to patch together from different codes I found in the MySQL forum. I added comments below as to make things clearer. I named the function splitAndTranslate since that’s what I was really trying to implement. You can make up your own modifications and function name.
DROP FUNCTION IF EXISTS `splitAndTranslate` //
CREATE FUNCTION splitAndTranslate(str TEXT, delim VARCHAR(124))
DECLARE i INT DEFAULT 0; -- total number of delimiters
DECLARE ctr INT DEFAULT 0; -- counter for the loop
DECLARE str_len INT; -- string length,self explanatory
DECLARE out_str text DEFAULT ''; -- return string holder
DECLARE temp_str text DEFAULT ''; -- temporary string holder
DECLARE temp_val VARCHAR(255) DEFAULT ''; -- temporary string holder for query
-- get length
SET i = (LENGTH(str)-LENGTH(REPLACE(str, delim, '')))/LENGTH(delim) + 1;
-- get total number delimeters and add 1
-- add 1 since total separated values are 1 more than the number of delimiters
-- start of while loop
-- add 1 to the counter, which will also be used to get the value of the string
-- get value separated by delimiter using ctr as the index
SET temp_str = REPLACE(SUBSTRING(SUBSTRING_INDEX(str, delim, ctr), LENGTH(SUBSTRING_INDEX(str, delim,ctr - 1)) + 1), delim, '');
-- query real value and insert into temporary value holder, temp_str contains the exploded ID
SELECT <real_value_column> INTO temp_val FROM <my_table> WHERE <table_id>=temp_str;
-- concat real value into output string separated by delimiter
SET out_str=CONCAT(out_str, temp_val, ',');
-- end of while loop
-- trim delimiter from end of string
SET out_str=TRIM(TRAILING delim FROM out_str);
RETURN(out_str); -- return
After creating the stored function, you can now use it normally like any MySQL function inside a query. So what I now do with the new function is…
SELECT splitAndTranslate( g.comma_separated_ids ) real_values FROM my_group_table g;
Thanks to Chris Stubben in the MySQL Forum, I used and modified his code to fit my need.
These are the steps I took to install Jakarta Tomkat 5.5 in conjunction with Java 2 SDK in Ubuntu server.
- Login as root, you can also use “su” though I prefer to login as root.
- apt-get install sun-java5-jdk
apt-get install tomcat5.5 tomcat5.5-admin tomcat5.5-webapps
- This will install Java 2 SDK (1.5), ubuntu will start downloading packages that are not found in your system.
Now here’s the tricky part, location for Java and jakarta-tomcat
- Of course jakarta-tomcat 5.5, I’m using 5.5 since this supports java 1.5
Now, open .bashrc in your favorite text editor, I used vim
At the end of the file add these:
- Java’s location is in /usr/lib/jvm/java-1.5.0-sun
- Jakarta-Tomcat’s location is in /usr/share/tomcat5.5
- We will need these location for the export configurations to be written in the .bashrc
Now save the file and exit, then log back in. This is required for the export script to be set.
Before starting the server, the default port the installer set is 8180 instead of the 8080 port that Tomcat uses. To change this, go to /usr/share/tomcat5.5/conf/ and open the file server.xml. Locate the line:
...Connector port="8180" maxHttpHeaderSize="8192"...
and change 8180 to 8080. Save and exit. Now your ready to test the server.
Now try the server if it starts, /usr/share/tomcat5.5/bin/startup.sh You should see something like this:
Shutting down the server is just /usr/share/tomcat5.5/bin/shutdown.sh
Now, during installation of tomcat, Ubuntu automatically adds a startup and shutdown script for ubuntu to use as it starts up or shutsdown in /etc/init.d/ folder. Filename is tomcat5.5. As the server finishes starting up, you will notice tomcat isn’t running at all. One possible problem is that the script didn’t use the correct path for the java 2 sdk. You can check the boot log in /var/log/. Check if during boot up, tomcat5.5 encountered problems. For the problem stated above, you can fix this by going to /etc/default/ and edit the tomcat5.5 file. Locate the line:
Using CATALINA_BASE: /usr/share/tomcat5.5
Using CATALINA_HOME: /usr/share/tomcat5.5
Using CATALINA_TMPDIR: /usr/share/tomcat5.5/temp
Using JRE_HOME: /usr/lib/jvm/java-1.5.0-sun
remove the ‘#’ and change it to…
or wherever your java directory is.After that, restart the server and see if tomcat was successfully started.
Edit: Problem encountered:
- Tomcat does not load in Ubuntu 8.04
Found a little problem loading Tomcat 5.5 under Ubuntu 8.04, it either fails or white screen just appears. I don’t know what happened from 6.04 to 8.04 but once I compared the init.d/tomcat5.5 startup script from 6.04 and 8.04, there WERE changes to the scripts. I replaced the new tomcat5.5 script in 8.04 with the old one from 6.04 and the server started properly after a server restart. I don’t know why but this may have something to do with permissions and I have yet to trace the script.
- java.lang.ClassNotFoundException: org.apache.jasper.tagplugins.jstl.If
- The problem here is that the above name is incomplete… what it should have been is org.apache.jasper.tagplugins.jstl.core.*
- Now, to fix the problem, locate
/var/lib/tomcat5.5/webapps/jsp-examples/WEB-INF/tagPlugins.xml and open it with your text editor… I used vim. Now edit each line of code that has org.apache.jasper.tagplugins.jstl in it and add “.core” after jstl. What you will see after editing the code will be…
- SEVERE: The scratchDir you specified: [folder_path] is unusable.
- Sidenote: took me 2 days to figure out why this was happening (X_x)
- Based from the Catalina logs, the folders under webapps was not accessible by tomcat5.
- Now looking under all processes running ( ps command ), most bootup services were running under root (mysql, apache, etc ) but tomcat5 was not.
- If I start tomcat5 when I logged into the console as root, the problem disappears. This lead me to believe this might have been the Tomcat5 user was not given the correct privileges.
- Work-around 1: Elevate Tomcat5 user to root access level.
- Work-around 2: Go to /etc/init.d/ and open Tomcat5.5 under any text editor ( I used vim ). Locate the line TOMCAT5_USER=tomcat55 and change it to TOMCAT5_USER=root . Restart your server or you can also execute the restart command for Tomcat5.5 in init.d folder