uac - Unaligned Access Message Control
uac p|s [value]
uac p|s [keyword]
The following options are used with the uac command: Sets or displays the current option setting for the parent process Sets or displays the current option setting for the system
The following keywords are used with the p option: Reset the current option settings to the default for the parent process Do not print the unaligned access warning message for the parent process Do not fix the unaligned access for the parent process Deliver a SIGBUS signal to the parent process
The following keywords are used with the s option: Reset the current option settings to the default for the system Do not print the unaligned access warning message for the system
Usually, the parent process is the shell.
Most complex instruction set computers (CISC) can access unaligned data but only at a significantly reduced speed. Most reduced instruction set computers (RISC) do not attempt to handle unaligned accesses. Instead, they generate an unaligned access trap and let the operating system handle the fault.
The default action for the operating system when an unaligned access fault occurs is to fix the unaligned access fault and then display a warning message informing the user process that an unaligned access fault has occurred. The warning message has the following form: ``Unaligned access pid=nnn <prog_name> va=virtual_addr pc=pc_addr''. If you want to change the code to prevent the unaligned access faults from occurring in the future, the warning message gives you the information you need to locate the code causing a fault. (See the Programmer's Guide for details on the causes and effects of misaligned data.)
In addition, the default action for the operating system is to not deliver a SIGBUS signal to the parent process when an unaligned access fault occurs.
These defaults are satisfactory for most users, but some users require a different behavior and want to specify their own Unaligned Access Control (UAC).
The uac command enables or disables the display of ``Unaligned access'' messages. The command sets or displays the UAC_NOPRINT, UAC_NOFIX, and UAC_SIGBUS options, as defined in setsysinfo(2).
If value is not specified, the current option setting is displayed. You can specify value as either 0 (zero) or 1 (one). If value is 0 (zero), the option is turned on and messages are not displayed. If value is 1 (one), the option is turned off and messages are displayed.
Keywords can be used singly, or in any combination. However, the
keyword overrides any other keywords it is used with.
You must be superuser to set the system option.
Both of the following commands disable messages for the parent process: # uac p 0