Use of truss and lsof in Unix

First command is truss.
The truss utility executes the specified command and produces a trace of the system calls it performs, the signals it receives, and the machine faults it incurs.
Each line of the trace output reports either the fault or signal name or the system call name with its arguments and return value(s).The command can be used as::: truss ./abc [abc is executable program]On following link you can find examples of the same.
http://www.ibm.com/developerworks/aix/library/au-unix-tracingapps.html
Another useful command is lsof.
lsof lists all the open files used by all the programs.
An open file may be a regular file, a directory, a block special file, a character special file, an executing text reference, a library, a stream or a network file.lsof can also be used to retrieve accidently deleted files, if they are currently being used by any process.On following link you can find examples of the same.
http://www.ibm.com/developerworks/aix/library/au-lsof.html?S_TACT=105AGX20&S_CMP=EDU