0 * * * * wget -q -O - http://www.example.com/notify.php >/tmp/cron 2>&1

In Linux, wget is used to download file from internet (or network). -q option means quiet, -O means output file. It is important to put the -O option so that your server won’t end up with annoying CRON output file.

1. Download tomcat and rename the file name from tomcat.doc to tomcat only (remove the extension)
2. Put the file under /etc/inid.d
3. Give execute privilege to the file (chmod +x /etc/init.d/tomcat)
4. Adjust 2 parameters in the file, TOMCAT and JAVA_HOME.
5. Add the file into service list (chkconfig ––add tomcat)
6. Done!

To do this, follow the steps:

1. Shutdown the database either using service or sql statement: shutdown immediate.
2. Copy or move the database to /db2 and rename the new database directory to mydb2.
3. Edit the initialize parameter file in the mydb2 (something like initxxx.ora), change the all the paths to the new path (from /db/mydb to /db2/mydb2)
4. Log in to sqlplus with NOLOG (run in terminal): sqlplus /nolog
5. Connect to empty instance (run in SQLPLUS): connection / as sysdba
6. Create SPFILE, aware that the path of the initialize parameter file might be vary (run in SQLPLUS): create spfile from pfile='/db2/mydb2/admin/pfile/initxxx.ora';
7. Start database in mount mode (run in SQLPLUS): startup mount;
8. Change the data file path to the new path (run in SQLPLUS): alter database rename file '/db/mydb/data.dbf', '/db/mydb/system.dbf' to '/db2/mydb2/data.dbf', '/db2/mydb2/system.dbf';
9. Ensure you change all the data file path! Or else it will cause the orginal database cannot be startup!
10. Open your database (run in SQLPLUS): alter database open;
11. Now it is good to go.

Here is a trick where I discover in order to recover the ROOT password in RHEL6.

1. First enter single user mode. To do this, boot your machine and wait until the message to enter GRUB (the one with a counter). Press any key to enter GRUB, then press e to edit the boot argument. Just append the word single at the back of the arguments and press enter to continue boot.
2. You should enter single user mode, with the root prompt. Instead of using entering only passwd, enter the following command:passwd -d root
3. “-d” is meant for making the password blank. Now your root password should be blank. Reboot your machine and change your ROOT password.

It is happened at an old HPUX machine with disk array attached. After 2 of the hard disks in the disk array are being replaced, the new hard disks cannot be seen in SAM. To discover back the missing hard disks, issue the following command:

armdiscover <array alias>

After the command, you should able to see the hard disks in SAM, and even can see the unmounted partitions. However you wouldn’t able to do anything with it, either mount it, remove it or recreate it. You should get some errors like “can’t find /dev/dsk/cxtxdx”. Then issue the following command:

armdsp -s <array alias>

This command will show the hard disks path in the disk array. You will see that the path is not the same inside the error. The unmounted partitions are actually still referring to the old hard disk path, where you need to remove it using the following command:

vgreduce -l /dev/vgxx /dev/dsk/cxtxdx

You must include “-l” in the command to remove the missing path. After that you need to add back the actual hard disk path either using SAM or vgextend command, and everything should be back to normal.

SET GLOBAL general_log = 'ON';

Or add following option to MySQL start up command (to turn off use 0):

mysqld --general_log=1

You can find the trace log at the database folder. The file name is something like host_name.log.

1. Create a trace log table. For example:

   CREATE TABLE TRACELOG
   (
      SESSION_ID        NUMBER(20),
      SESSION_USER      VARCHAR2(30 BYTE),
      OS_USER           VARCHAR2(30 BYTE),
      HOST              VARCHAR2(30 BYTE),
      IP_ADDRESS        VARCHAR2(30 BYTE),
      TERMINAL          VARCHAR2(30 BYTE),
      MODULE            VARCHAR2(30 BYTE),
      LAST_ACTION       VARCHAR2(32 BYTE),
      LAST_ACTION_DATE  DATE,
      LOGON_DATE        DATE,
      LOGOFF_DATE       DATE
   )

2. Grand privilege to public to update the TRACELOG table

   GRANT INSERT, UPDATE, SELECT ON TEMP_TRACE TO PUBLIC;

3. Create Log On Trigger. For example:

   CREATE OR REPLACE TRIGGER on_logon_trigger
   after logon on database
   begin
      insert into tracelog(session_id, session_user, os_user, host, ip_address, terminal, module, logon_date)
      SELECT sys_context('USERENV', 'sessionid'),
      user,
      sys_context('USERENV', 'os_user'),
      sys_context('USERENV', 'host'),
      sys_context('USERENV', 'ip_address'),
      sys_context('USERENV', 'terminal'),
      sys_context('USERENV', 'module'),
      sysdate
      FROM dual;
      commit;
   end;

4. Create Log Off Trigger. For example:

   CREATE OR REPLACE TRIGGER on_logoff_trigger
   before logoff on database
   begin
      update tracelog
      set logoff_date = sysdate
      where session_id = sys_context('USERENV', 'sessionid')
      and logoff_date is null;
      commit;
   end;

Now you can trace user access by querying the TRACELOG table.

1. Put your new android installation file in SD Card (it will be in ZIP file)
2. Boot your phone in Recover Tool
3. Do a Backup, just in case (it will backup everything inside your internal memory)
4. Wipe your phone internal memory (normally MUST if you are flashing a completely different Android, but if it is upgrade or downgrade of the same Android, probably can skip)
5. Then install zip file from SD Card
6. Reboot and done

The only painful thing of flashing is that you might need to reconfigure everything and install back what application you want (just like format a PC). So the more tricky part is to pick the correct one. You can only know this version of Android is your favorite or not until you use it, and switching between different Android is troublesome.

The customized Android is roughly divided by 2 types: Android with HTC Sense UI, and Android with AOSP UI. After choosing the UI that you want, then choose the version based on the application that come with it.

Some major player of customized Android include cyanogenmod, defrost, oxygen and some more.

My favorite comparison chart on customized Android

Basic Understanding on How Android Works

Android is Linux

This might be obvious but I point this out any way. So if you browse the file system using any file manager, you can see the file structure is following Linux style: /system, /data, /cache, /mnt and some more. Since it is Linux, Android is using EXT as hard disk format (Froyo using EXT3 while Gingerbread using EXT4).

ROM, Internal Memory, Memory and SD Card

We always heard of flashing ROM in Android, which the term is not exactly correct. Most of the time we are actually flashing the internal memory. Like a PC, Android boots from HBOOT (equivalent to BIOS) that stay at ROM, then loads the system files from Internal Memory, and lastly loads any applications that installed to SD Card.

Not sure what kind of format is used in ROM, but roughly it is partitioned into few partitions like HBOOT, RECOVERY and SPLASH1

Internal Memory is definitely in EXT format that partitioned into few partitions as well. The main partitions are SYSTEM (basically where Android files stay), CACHE and DATA (where application installed). So if you check the Internal Memory size from Settings, you might be confused by the size of it (much lower than the specification). Actually the size showed is the size of DATA partition, while the rest of the size is used by other partitions.

Lastly SD Card is in FAT format.

Rooting, Recovering and Flashing

Rooting in Android is more than gaining back the root privilege. In order to protect the phone from user, manufacturer puts a lot of security features to the ROM and Internal Memory. So rooting is actually mean disable the security features.

Aside from disable the security, rooting also includes step to install a recover tools in ROM. By using the recover tools, user can flash the internal memory with other version of Android (just boot into HBOOT and select to boot from recover, like multi boot in PC).

Unrevoked provides tool to do rooting for HTC.

S-OFF and Repartition

However flashing the internal memory only put in the new system files, but it cannot repartition it (you might want to have a bigger size of DATA partition to install more application). To do repartition, we need to do S-OFF and patch HBOOT. After S-OFF and the patching, we now can have the options to repartition by flashing HBOOT in ROM.

AlphaRev provides tool to do S-OFF and repartition for HTC.

1. Generate a key store file using keytool utility (installed together with JDK). It will ask for a password to generate the key store file.
   keytool -genkey -alias <any alias name> -keyalg RSA -keystore <output file>
   For example:
   keytool -genkey -alias tomcat -keyalg RSA -keystore tomcat.key
2. Generate a certificate request file.
   keytool -certreq -keyalg RSA -alias <alias> -file <output file> -keystore <keystore file>
   Example:
   keytool -certreq -keyalg RSA -alias tomcat -file certreq.csr -keystore tomcat.key
3. Then submit the certificate request to your CA. Normally you just need to submit the content of the request file.
4. As a result you will get the content of the certificate. Copy the content and save it as a certificate file (for example tomcat.cer)
5. For some CA (like Thawte), you need to download the CA trusted certificate from the their website in order to complete the implementation (EV_Root.cer and EV_intermediate.cer)
6. Finally import the certificates using command below:
   keytool -import -alias <alias name> -keystore <keystore file> -trustcacerts -file <certificate>
   For example:
   keytool -import -alias EV_Root -keystore online.key -trustcacerts -file EV_Root.cer
keytool -import -alias EV_intermediate -keystore online.key -trustcacerts -file EV_intermediate.cer
keytool -import -alias tomcat -keystore tomcat.key -trustcacerts -file tomcat.cer

Some references to retrieve private key from the key store that you generate.