Kernel
/proc Filesystem
/dev Filesystem
Lab
ATOL: Kernel Services
Marek Grác
xgrac@fi.muni.cz
Red Hat Czech s.r.o. / Faculty of Informatics, Masaryk University
Advanced Topics of Linux Administration
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Kernel Images and Variants
Architectures supported: x86, x86-64, IA64, PowerPC64,
s390x
Three kernel versions available for x86:
Regular: one or more processsors but 4GB of RAM or less
PAE (big-iron): multiple processors and up to 64GB of RAM
Xen: needed for virtualization
Kernel always installed under /boot/vmlinuz-*
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Kernel Modules
Modules are small kernel extensions that may be loaded and
unloaded at will
Can implement drivers, filesystems, firewall, and more
Are located under /lib/modules/(uname -r)/
Compiled for a specific kernel version and area provided with
the kernel package
Third party modules may be added
Tainted modules ­ 3rd party non-GPL modules
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Kernel Modules Utilities
lsmod provides a list of loaded modules
modprobe can load and unload modules
/etc/modprobe.conf used for module configuration:
Parameters to pass to a module whenever it is loaded
Aliases to represent a module name
Commands to execute when a module is loaded or unloaded
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
/proc Filesystem
/proc used to get or set kernel configuration
Virtual filesystem: files not stored on hard disk
Entries not persistent: modifications get reinitialized after a
reboot
Used to display process information, memory resources,
hardware devices, kernel memory, etc.
Can be used to modify network and memory subsystems or
modify kernel features
Modifications apply immediately
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
/proc Examples
Read-only files
/proc/cpuinfo
/proc/1/*
/proc/partitions
/proc/meminfo
Read-write files
/proc/sys/kernel/hostname
/proc/sys/net/ipv4/ip forward
/proc/sys/vm/drop caches
/proc/sys/vm/swappiness
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
sysctl : Persistent Kernel Configuration
sysctl adds persistence to /proc/sys settings
Statements added to /etc/sysctl.conf automatically
reflected under /proc after a reboot
Configuration maintained or monitored using the sysctl
commands:
List all current settings: sysctl -a
Reload settings from sysctl.conf: sysctl -p
Set a /proc value dynamically: sysctl -w net.ipv4.ip forward=1
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Accessing Drivers Through /dev
Files under /dev used to access drivers
Reading from and writing to those files are valid operations:
Read from serial port: cat /dev/ttyS0
Write to serial port: echo Message > /dev/ttyS0
Three files attributes determine which driver to access:
Device type (character or block)
Major number
Minor number
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Device Node Examples
Block Devices
/dev/hda, /dev/hdc ­ IDE hard disk, CDROM
/dev/sda, /dev/sdc ­ SCSI, SATA, or USB Storage
/dev/md0, /dev/md1 ­ Software RAID
Character Devices
/dev/tty[0-6] ­ virtual Consoles
/dev/null, /dev/zero ­ software Devices
/dev/random, /dev/urandom ­ random Numbers
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Managing /dev with udev
udev manages files stored under /dev/
Files only created if corresponding device is plugged in
Files are automatically removed when the device is
disconnected
udev statements under /etc/udev/rules.d determine:
Filenames
Permissions, Owners and groups
Commands to execute when a new device shows up
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Adding Files Under /dev
The right way to add a /dev entry involes udev:
Create a new file under /etc/udev/rules.d
Insert a statement such as:
KERNEL==sda, NAME=usbkey, SYMLINK=usbstorage
This creates a device file named usbkey and a symlink named
usbstorage next time /dev/sda gets plugged.
Files can be added manually with mknod:
mknod /dev/usbdevice b 8 0
mknod not persistent !
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Exploring Hardware Devices
A snapshot of all connected devices is maintained by HAL
HAL is acronym for Hardware Abstraction Layer
hal-device lists all devices in text mode.
hal-device-manager displays all devices on a graphical window.
lspci and lsusb list devices connected to the PCI and USB
buses, respectively.
The /proc and /sys filesystems also contains bus and device
specific information.
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
Kernel
/proc Filesystem
/dev Filesystem
Lab
Lab: Installation
Goals:
A system that does not respond to ping
A system that provides /dev/myusbdisk automatically after a
reboot.
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services
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/proc Filesystem
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Lab: Prepare a paper
Themes:
Describe features of HAL
Kernel modules: tuning and performance
Format:
Short presentation (15­20 minutes; 5-7 slides)
Paper containing comparision (500 words)
Marek Grác xgrac@fi.muni.cz ATOL: Kernel Services