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sysfs.md

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sysfs

Similar to proc, but contains other system information besides processes.

Mounted by default under /sys.

Like proc, is a regular filesystem, that is listed under /proc/filesystems and can be mounted multiple times.

Like proc, it is not possible to create files under it: sudo touch /sys/a fails.

/sys/bus/pci/devices

/sys/bus/pci_express/devices

http://prefetch.net/articles/linuxpci.html

PCI bus information.

lspci is a good way to extract human readable information from those directories.

ls /sys/bus/pci/devices | head -n 4

gives something like:

lrwxrwxrwx 1 root root 0 Apr 19 08:34 0000:00:00.0 -> ../../../devices/pci0000:00/0000:00:00.0
lrwxrwxrwx 1 root root 0 Apr 19 08:34 0000:00:01.0 -> ../../../devices/pci0000:00/0000:00:01.0
lrwxrwxrwx 1 root root 0 Apr 19 08:34 0000:00:02.0 -> ../../../devices/pci0000:00/0000:00:02.0
lrwxrwxrwx 1 root root 0 Apr 19 08:34 0000:00:14.0 -> ../../../devices/pci0000:00/0000:00:14.0

Breaking down an ID of form 0000:01:02.3

  • 0000: PCI domain (each domain can contain up to 256 PCI buses)
  • 01: the bus number the device is attached to
  • 02: the device number
  • 3: PCI device function

If we go then under one of the directories and ls:

ls -l /sys/bus/pci/devices/0000:00:00.0

Output:

total 0
drwxr-xr-x 2 root root    0 Apr 19 06:35 power
-rw-r--r-- 1 root root 4096 Apr 19 10:09 broken_parity_status
-r--r--r-- 1 root root 4096 Apr 19 06:35 class
-rw-r--r-- 1 root root  256 Apr 19 06:35 config
-r--r--r-- 1 root root 4096 Apr 19 10:09 consistent_dma_mask_bits
-rw-r--r-- 1 root root 4096 Apr 19 10:09 d3cold_allowed
-r--r--r-- 1 root root 4096 Apr 19 06:35 device
-r--r--r-- 1 root root 4096 Apr 19 10:09 dma_mask_bits
-rw-r--r-- 1 root root 4096 Apr 19 10:09 enable
-r--r--r-- 1 root root 4096 Apr 19 06:35 irq
-r--r--r-- 1 root root 4096 Apr 19 10:09 local_cpulist
-r--r--r-- 1 root root 4096 Apr 19 10:09 local_cpus
-r--r--r-- 1 root root 4096 Apr 19 10:09 modalias
-rw-r--r-- 1 root root 4096 Apr 19 10:09 msi_bus
-r--r--r-- 1 root root 4096 Apr 19 10:09 numa_node
--w--w---- 1 root root 4096 Apr 19 10:09 remove
--w--w---- 1 root root 4096 Apr 19 10:09 rescan
-r--r--r-- 1 root root 4096 Apr 19 06:35 resource
lrwxrwxrwx 1 root root    0 Apr 19 06:36 subsystem -> ../../../bus/pci
-r--r--r-- 1 root root 4096 Apr 19 10:09 subsystem_device
-r--r--r-- 1 root root 4096 Apr 19 10:09 subsystem_vendor
-rw-r--r-- 1 root root 4096 Apr 19 08:34 uevent
-r--r--r-- 1 root root 4096 Apr 19 06:35 vendor

Some interesting files:

cat class vendor device

Sample output:

0x060000
0x8086
0x0154

Those IDs can be decoded with the /usr/share/hwdata/pci.ids file.

/usr/share/hwdata/pci.ids

We can then find what PCI IDs correspond to with:

less /usr/share/hwdata/pci.ids

which is provided by the hwdata package https://git.fedorahosted.org/hosted/hwdata.git/. If we search for ^8086 we find:

8086 Intel Corporation
    0154  3rd Gen Core processor DRAM Controller

TODO:

  • why do many devices are shown under PCI, but I think PCI was replaced by PCIe a long time ago.

update-pciid

Updates

/sys/block

Block devices.

Convenience only: all device directories point to /sys/devices

https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-block

removable

http://unix.stackexchange.com/questions/125961/how-to-tell-if-a-scsi-device-is-removable

TODO what does it mean exactly? My main hard disk was not removable, but my USB was:

cat /sys/block/sda/removable
cat /sys/block/sdb/removable

/sys/class

Devices grouped by category.

This is only for convenience: all device directories are symlinks to /sys/devices.

E.g.:

ls -l /sys/class/rtc/

Gives the rtc0 device directory:

total 0
lrwxrwxrwx 1 root root 0 Sep 25 09:46 rtc0 -> ../../devices/pnp0/00:02/rtc/rtc0

Bibliography

http://prefetch.net/articles/linuxpci.html