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Chapter 22.
Additional Information for IBM System
z Users
22.1. The sysfs File System
The Linux 2.6 kernel introduced the sysfs file system. The sysfs file system is described as a union
of the proc, devfs, and devpty file systems. The sysfs file system enumerates the devices and
busses attached to the system into a file system hierarchy that can be accessed from user space. It is
designed to handle the device and driver specific options that have previously resided in /proc/, and
encompass the dynamic device addition previously offered by devfs.
The sysfs file system is mounted at /sys/ and contains directories that organize the devices
attached to the system in several different ways. The /sysfs/ subdirectories include:
1. The /devices/ directory
This directory contains the /css0/ directory. Its subdirectories represent all the subchannels
detected by the Linux kernel. Subchannel directories are named in the form 0.0.nnnn where
nnnn is the subchannel number in hex between 0000 and ffff. Subchannel directories in turn
contain status files and another subdirectory which represents the actual device. The device
directory is named 0.0.xxxx where xxxx is the unit address for the device. The /devices/
directory also contains status information as well as configuration options for the device.
2. The /bus/ directory
This contains a /ccw/ subdirectory and a /ccwgroup/ subdirectory. CCW devices are accessed
using channel command words. Devices in the /ccw/ directory only use one subchannel on the
mainframe channel subsystem. CCW group devices are also accessed with channel command
words, but they use more than one subchannel per device. For example, a 3390-3 DASD
device uses one subchannel, while a QDIO network connection for an OSA adapter uses three
subchannels. The /ccw/ and the /ccwgroup/ directories both contain directories called devices
and drivers:
The /devices/ directory contains a symbolic link to the device directories in the /sys/
devices/css0/ directory.
The /drivers/ directory contains directories for each device driver currently loaded on the
system. Drivers associated with devices such as dasd, console, qeth, and zfcp have directory
entries here. The /driver/ directory contains settings for the device driver, as well as symbolic
links to the devices it is using (in the /sys/devices/css0/ directory).
3. The /class/ directory
This contains directories that group together similar devices such as ttys, SCSI tape drives,
network devices, and other miscellaneous devices.
4. The /block/ directory
This directory contains directories for each of the block devices on the system. These are mostly
disk type devices such as real DASD, loopback devices, and software raid block devices. The
noticeable difference between older Linux systems and ones that use sysfs is the need to refer
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Table of Contents
Troubleshooting
