Sun Studio 12: Debugging a Program With dbx

Setting dbx Environment Variables

You can use the dbxenv command to set the dbx environment variables that customize your dbx sessions.

To display the value of a specific variable, type:

(dbx) dbxenv variable

To show all variables and their values, type:

(dbx) dbxenv

To set the value of a variable, type:

(dbx) dbxenv variable value

Table 3–1 shows all of the dbx environment variables that you can set:

Table 3–1 dbx Environment Variables

dbx Environment Variable

What the Variable Does  

array_bounds_check on|off

If set to on, dbx checks the array bounds.

Default: on.


Lets you specify to dbx a path for Java class files that are loaded by custom class loaders

core_lo_pathmap on|off

Controls whether dbx uses pathmap settings to locate the correct libraries for a “mismatched” core file. Default: off.


Sets global debug file directory. Default: /usr/lib/debug.

disassembler_version autodetect|v8|v9|x86_32|x86-64

SPARC platform: Sets the version of dbx’s built-in disassembler for SPARC V8 or V9. Default is autodetect, which sets the mode dynamically depending on the type of the machine a.out is running on.

x86 platforms: The valid choice is autodetect.


Protects dbx against unsafe use of events.

fix_verbose on|off

Governs the printing of compilation line during a fix. Default: off

follow_fork_inherit on|off

When following a child, inherits or does not inherit breakpoints. Default: off

follow_fork_mode parent|child|both|ask

Determines which process is followed after a fork; that is, when the current process executes a fork, vfork, or fork1. If set to parent, the process follows the parent. If set to child, it follows the child. If set to both, it follows the child, but the parent process remains active. If set to ask, you are asked which process to follow whenever a fork is detected. Default: parent.

follow_fork_mode_inner unset|


Of relevance after a fork has been detected if follow_fork_mode was set to ask, and you chose stop. By setting this variable, you need not use cont -follow.

input_case_sensitive autodetect|


If set to autodetect, dbx automatically selects case sensitivity based on the language of the file: false for Fortran files, otherwise true. If true, case matters in variable and function names; otherwise, case is not significant.

Default: autodetect.


Specifies the directories in which dbx should look for Java source files.

jdbx_mode java| jni| native

Stores the current dbx mode. It can have the following settings: java, jni, or native.


The jvm_invocation environment variable lets you customize the way the JVMTM software is started. (The terms “Java virtual machine” and “JVM” mean a virtual machine for the JavaTM platform.) For more information, see Customizing Startup of the JVM Software.

language_mode autodetect|main|c| c++|fortran|fortran90

Governs the language used for parsing and evaluating expressions. 

  • autodetect sets the expression language to the language of the current file. Useful if debugging programs with mixed languages (default).

  • main sets the expression language to the language of the main routine in the program. Useful if debugging homogeneous programs.

  • c, c++, c++, fortran, or fortran90 sets the expression language to the selected language.

mt_scalable on|off

When enabled, dbx will be more conservative in its resource usage and will be able to debug processes with upwards of 300 LWPs. The down side is significant slowdown. Default: off.

optim_local_vars on|off

When enabled, you can evaluate local variables in optimized functions. Default: off.

output_auto_flush on|off

Automatically calls fflush() after each call. Default: on

output_base 8|10|16|automatic

Default base for printing integer constants. Default: automatic (pointers in hexadecimal characters, all else in decimal).

output_class_prefix on | off

Used to cause a class member to be prefixed with classname(s) when its value or declaration is printed. If set to on, it causes the class member to be prefixed. Default: on.

output_dynamic_type on|off

When set to on, -d is the default for printing watches and displaying. Default: off.

output_inherited_members on|off

When set to on, -r is the default for printing, displaying, and inspecting. Default: off.

output_list_size num

Governs the default number of lines to print in the list command. Default: 10.

output_log_file_name filename

Name of the command logfile. 

Default: /tmp/dbx.log.uniqueID

output_max_string_length number

Sets number of characters printed for char *s. Default: 512.


When enabled, if the expression is a string (char *), print the address only, do not print the literal. Default: off.

output_pretty_print on|off

Sets -p as the default for printing watches and displaying. Default: off.


By default, pretty-printing reverts to regular printing if problems occur. If you want to diagnose a pretty-printing problem, set this variable to off to prevent the fallback. Default: on

output_short_file_name on|off

Displays short path names for files. Default: on.

overload_function on|off

For C++, if set to on, does automatic function overload resolution. Default: on.

overload_operator on|off

For C++, if set to on, does automatic operator overload resolution. Default: on.

pop_auto_destruct on|off

If set to on, automatically calls appropriate destructors for locals when popping a frame. Default: on.

proc_exclusive_attach on|off

If set to on, keeps dbx from attaching to a process if another tool is already attached. Warning: be aware that if more than one tool attaches to a process and tries to control it chaos ensues. Default: on.

rtc_auto_continue on|off

Logs errors to rtc_error_log_file_name and continue. Default: off.

rtc_auto_suppress on|off

If set to on, an RTC error at a given location is reported only once. Default: off.

rtc_biu_at_exit on|off|verbose

Used when memory use checking is on explicitly or via check -all. If the value is on, a non-verbose memory use (blocks in use) report is produced at program exit. If the value is verbose, a verbose memory use report is produced at program exit. The value off causes no output. Default: on.

rtc_error_limit number

Number of RTC errors to be reported. Default: 1000.

rtc_error_log_file_name filename

Name of file to which RTC errors are logged if rtc_auto_continue is set. Default:


rtc_error_stack on|off

If set to on, stack traces show frames corresponding to RTC internal mechanisms. Default: off.

rtc_inherit on|off

If set to on, enables runtime checking on child processes that are executed from the debugged program and causes the LD_PRELOAD environment variable to be inherited. Default: off.

rtc_mel_at_exit on|off|verbose

Used when memory leak checking is on. If the value is on, a non-verbose memory leak report is produced at program exit. If the value is verbose, a verbose memory leak report is produced at program exit. The value off causes no output. Default: on.

run_autostart on|off

If set to on with no active program, step, next, stepi, and nexti implicitly run the program and stop at the language-dependent main routine. If set to on, cont implies run when necessary.

Default: off.

run_io stdio|pty

Governs whether the user program’s input/output is redirected to dbx’s stdio or a specific pty. The pty is provided by run_pty. Default: stdio.

run_pty ptyname

Sets the name of the pty to use when run_io is set to pty. Ptys are used by graphical user interface wrappers.

run_quick on|off

If set to on, no symbolic information is loaded. The symbolic information can be loaded on demand using prog -readsysms. Until then, dbx behaves as if the program being debugged is stripped. Default: off.

run_savetty on | off

Multiplexes tty settings, process group, and keyboard settings (if -kbd was used on the command line) between dbx and the program being debugged. Useful when debugging editors and shells. Set to on if dbx gets SIGTTIN or SIGTTOU and pops back into the shell. Set to off to gain a slight speed advantage. The setting is irrelevant if dbx is attached to the program being debugged or is running in the Sun Studio IDE. Default: off.

run_setpgrp on | off

If set to on, when a program is run, setpgrp(2)is called right after the fork. Default: off.

scope_global_enums on | off

If set to on, enumerators are put in global scope and not in file scope. Set before debugging information is processed (~/.dbxrc). Default: off.

scope_look_aside on | off

If set to on, finds file static symbols, in scopes other than the current scope. Default: on.

session_log_file_name filename

Name of the file where dbx logs all commands and their output. Output is appended to the file. Default: "" (no session logging).

stack_find_source on | off

When set to on, dbx attempts to find and automatically make active the first stack frame with source when the program being debugged comes to a stop in a function that is not compiled with -g.

Default: on.

stack_max_size number

Sets the default size for the where command. Default: 100.

stack_verbose on | off

Governs the printing of arguments and line information in where. Default: on.

step_abflow stop|ignore

When set to stop, dbx stops in longjmp(), siglongjmp(), and throw statements when single stepping. When set to ignore, dbx does not detect abnormal control flow changes for longjmp() and siglongjmp().

step_events on |off

When set to on, allows breakpoints while using step and next commands to step through code. Default: off.

step_granularity statement | line

Controls granularity of source line stepping. When set to statement the following code:

a(); b();

takes the two next commands to execute. When set to line a single next command executes the code. The granularity of line is particularly useful when dealing with multiline macros. Default: statement.

suppress_startup_message number

Sets the release level below which the startup message is not printed. Default: 3.01. 

symbol_info_compression on|off

When set to on, reads debugging information for each include file only once. Default: on.

trace_speed number

Sets the speed of tracing execution. Value is the number of seconds to pause between steps. 

Default: 0.50.