nvram(7) nvram(7)
NAME
nvram - non-volatile memory/time of day clock interface
DESCRIPTION
The device /dev/nvram provides access to the real time clock
chip on the Oreo system board. This chip contains 256 bytes
of non-volatile memory (memory that retains its contents
when the system's power is turned off). It also contains a
time of day clock.
The special device /dev/nvram can be read by anyone. It
returns up to 260 bytes. The first 256 bytes are the
contents of the non-volatile ram; the next four are the
contents of the time of day clock. The time is in seconds
and the most significant byte comes first (byte #256). The
least significant comes last (byte #259). All four bytes of
the time should always be read or written at the same time
or the results are unpredictable. In order to write to
/dev/nvram one must be the super-user (root).
If the device is already open an attempt to open it will
return the error EBUSY. This is to ensure that a process
can perform read-modify-write operations on the device. If
an open fails with EBUSY the process should wait a while and
then try again. After an open suceeds the device should be
kept open only as long as is necessary.
WARNING: Care should be taken in writing this device. Since
the contents of the non-volatile ram are defined by Apple
and used by many parts of both UNIX ® and the Macintosh
operating system, indiscriminate writing could cause your
system to malfunction. Usually you should use the utilities
provided to manipulate the nvram contents.
FILES
/dev/nvram
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