QNX RTOS v4 Knowledge Base
QNX RTOS v4 Knowledge Base
| Title |
Disk writes and the /dev directory |
| Ref. No. |
QNX.000004448 |
| Category(ies) |
Utilities, Configuration |
| Issue |
If we power down during a boot we sometimes irreparably damage the root file system. The only writing to disk that occurs during boot seems to be the creation of the /dev directory.
It is impossible to guarantee that a power down will not occur during boot in our application.
Is it possible to mount the /dev directory on a different partition other than the root? The /dev directory and all its entries seem to be created at boot time. How much control do we have to move it, or limit the entries?
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| Solution |
The entries to Dev may be controlled by using the -n/-N options. Typing 'use Dev' shows:
Dev [-n devices] &
Options:
-n devices Maximum number of devices to support (default: 64).
-N prefix Name to register in the pathname space (default: /dev)
Examples:
Dev & - Start Dev using defaults.
Dev -n 100 & - Allow 100 devices.
Version: 423G
The /dev directory is not actually on disk, it is in the namespace only (in memory). Therefor a shutdown during a /dev creation at boot time will not damage the file system. For more information, read Chapter 4 I/O Namespace in the QNX OS System Architecture manual.
Running 'chkfsys' in your sysinit.node file DOES read/write to disk, and can cause problems if a powerdown occurs while chkfsys is running. Have a look at the documentation for this utility in the QNX OS Utilities A to M manual. |
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