Difference between revisions of "Kernel module"
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− | [[Category:Kernel | + | [[Category:Kernel]] |
− | [[Category:Hardware detection and troubleshooting | + | [[Category:Hardware detection and troubleshooting]] |
− | [[Category:Boot process | + | [[Category:Boot process]] |
− | {{ | + | [[es:Kernel modules]] |
+ | [[fr:Kernel modules]] | ||
+ | [[it:Kernel modules]] | ||
+ | [[ja:Kernel modules]] | ||
+ | [[zh-CN:Kernel modules]] | ||
+ | {{Article summary start}} | ||
+ | {{Article summary text|This article covers the various methods for operating with kernel modules.}} | ||
+ | {{Article summary heading|Related}} | ||
+ | {{Article summary wiki|Boot Debugging}} | ||
+ | {{Article summary wiki|Kernels}} | ||
+ | {{Article summary wiki|Kernel parameters}} | ||
+ | {{Article summary heading|Resources}} | ||
+ | {{Article summary link|modprobe man page|http://linuxmanpages.com/man5/modprobe.conf.5.php}} | ||
+ | {{Article summary end}} | ||
− | + | [[Wikipedia:Loadable_kernel_module|Kernel modules]] are pieces of code that can be loaded and unloaded into the kernel upon demand. They extend the functionality of the kernel without the need to reboot the system. | |
− | ==Overview== | + | == Overview == |
− | |||
− | |||
− | + | To create a kernel module, you can read [http://tldp.org/LDP/lkmpg/2.6/html/index.html this guide]. A module can be configured to be build-in or loadable. To dynamically load or remove a module, it has to be configured as a loadable module in the kernel configuration (the line related to the module will therefore display the letter {{ic|M}}). | |
− | + | Modules are stored in {{ic|/usr/lib/modules/''kernel_release''}}. You can use the command {{ic|uname -r}} to get your current kernel release version. | |
− | + | {{Note|Module names often use underscores ({{ic|_}}) or dashes ({{ic|-}}), however those symbols are interchangeable both when using the {{ic|modprobe}} command and in configuration files in {{ic|/etc/modprobe.d/}}.}} | |
− | + | == Obtaining information == | |
− | + | To show what kernel modules are currently loaded: | |
− | |||
$ lsmod | $ lsmod | ||
− | + | To show information about a module: | |
+ | |||
$ modinfo ''module_name'' | $ modinfo ''module_name'' | ||
− | + | To list the options that are set for a loaded module: | |
− | |||
− | |||
$ systool -v -m ''module_name'' | $ systool -v -m ''module_name'' | ||
− | + | To display the comprehensive configuration of all the modules: | |
− | |||
− | |||
$ modprobe -c | less | $ modprobe -c | less | ||
− | To display the configuration of a particular module | + | To display the configuration of a particular module: |
$ modprobe -c | grep ''module_name'' | $ modprobe -c | grep ''module_name'' | ||
− | ==Loading== | + | List the dependencies of a module (or alias), including the module itself: |
+ | |||
+ | $ modprobe --show-depends ''module_name'' | ||
+ | |||
+ | == Loading == | ||
+ | |||
+ | The {{ic|/sbin/modprobe}} command handles the addition and removal of modules from the Linux kernel. | ||
To manually load (or add) a module, run: | To manually load (or add) a module, run: | ||
# modprobe ''module_name'' | # modprobe ''module_name'' | ||
− | + | Most modules should be loaded on-demand. Modules to be unconditionally loaded at boot can be specified in {{ic|/etc/modules-load.d/}}, for example: | |
− | ==Removal== | + | {{hc|/etc/modules-load.d/virtio-net.conf| |
− | + | #Load 'virtio-net.ko' at boot. | |
+ | |||
+ | virtio-net}} | ||
+ | |||
+ | == Removal == | ||
+ | |||
+ | To remove (or unload) a module, use the following command: | ||
# modprobe -r ''module_name'' | # modprobe -r ''module_name'' | ||
Line 58: | Line 77: | ||
# rmmod ''module_name'' | # rmmod ''module_name'' | ||
− | == | + | == Configuration == |
− | To pass a parameter to a kernel module you can use a modprobe conf file or use the kernel command line. | + | |
+ | To pass a parameter to a kernel module you can use a modprobe conf file or use the kernel command line. See also [[Systemd#Kernel_modules]]. | ||
+ | |||
+ | === Using files in /etc/modprobe.d/ === | ||
+ | |||
+ | The {{ic|/etc/modprobe.d/}} directory can be used to pass module settings to [[udev]], which will use {{ic|modprobe}} to manage the loading of the modules during system boot. You can use configuration files with any name in the directory, given that they end with the {{ic|.conf}} extension. The syntax is: | ||
+ | {{hc|/etc/modprobe.d/myfilename.conf|2= | ||
+ | options modname parametername=parametercontents}} | ||
+ | |||
+ | For example: | ||
+ | |||
+ | {{hc|/etc/modprobe.d/thinkfan.conf|2= | ||
+ | #On Thinkpads, this lets the 'thinkfan' daemon control fan speed. | ||
− | |||
− | |||
− | |||
− | |||
− | |||
options thinkpad_acpi fan_control=1}} | options thinkpad_acpi fan_control=1}} | ||
− | ===Using kernel command line=== | + | {{Note|If any of the modules affected are loaded while booting (from the init ramdisk) then you will need to add the appropriate {{ic|.conf}}-file to FILES in [[mkinitcpio.conf]].}} |
− | If the module is built into the kernel you can also pass options to the module using the kernel command line | + | |
+ | === Using kernel command line === | ||
+ | |||
+ | If the module is built into the kernel you can also pass options to the module using the kernel command line. For all common Bootloaders the following syntax is correct: | ||
+ | |||
modname.parametername=parametercontents | modname.parametername=parametercontents | ||
+ | |||
for example: | for example: | ||
+ | |||
thinkpad_acpi.fan_control=1 | thinkpad_acpi.fan_control=1 | ||
− | ==Aliasing== | + | Simply add this to your bootloaders kernel-line as described in [[Kernel_parameters#When_starting_the_kernel|Kernel Parameters]]. |
− | + | ||
− | {{hc|/etc/modprobe.d/myalias.conf| | + | == Aliasing == |
− | + | ||
+ | Aliases are alternate names for a module. For example: "alias my-mod really_long_modulename" means you can use "modprobe my-mod" instead of "modprobe really_long_modulename". You can also use shell-style wildcards, so "alias my-mod* really_long_modulename" means that "modprobe my-mod-something" has the same effect. Create an alias: | ||
+ | |||
+ | {{hc|/etc/modprobe.d/myalias.conf| | ||
+ | alias mymod ''really_long_module_name''}} | ||
Some modules have aliases which are used to autoload them when they are needed by an application. Disabling these aliases can prevent auto-loading, but will still allow the modules to be manually loaded. | Some modules have aliases which are used to autoload them when they are needed by an application. Disabling these aliases can prevent auto-loading, but will still allow the modules to be manually loaded. | ||
− | |||
− | |||
− | # Prevent autoload | + | {{hc|/etc/modprobe.d/modprobe.conf| |
− | alias net-pf- | + | #Prevent Bluetooth autoload. |
+ | |||
+ | alias net-pf-31 off}} | ||
+ | |||
+ | == Blacklisting == | ||
− | |||
Blacklisting, in the context of kernel modules, is a mechanism to prevent the kernel module from loading. This could be useful if, for example, the associated hardware is not needed, or if loading that module causes problems: for instance there may be two kernel modules that try to control the same piece of hardware, and loading them together would result in a conflict. | Blacklisting, in the context of kernel modules, is a mechanism to prevent the kernel module from loading. This could be useful if, for example, the associated hardware is not needed, or if loading that module causes problems: for instance there may be two kernel modules that try to control the same piece of hardware, and loading them together would result in a conflict. | ||
− | Some modules are loaded as part of the [[initramfs]]. {{ic|mkinitcpio -M}} will print out all autodetected modules: to prevent the initramfs from loading some of those modules, blacklist them in {{ic|/etc/modprobe.d/modprobe.conf}}. Running {{ic|mkinitcpio -v}} will list all modules pulled in by the various hooks (e.g. filesystem hook, SCSI hook, etc.). Remember to rebuild the initramfs once you have blacklisted the modules and to reboot afterwards. | + | Some modules are loaded as part of the [[initramfs]]. {{ic|mkinitcpio -M}} will print out all autodetected modules: to prevent the initramfs from loading some of those modules, blacklist them in {{ic|/etc/modprobe.d/modprobe.conf}}. Running {{ic|mkinitcpio -v}} will list all modules pulled in by the various hooks (e.g. filesystem hook, SCSI hook, etc.). Remember to add that {{ic|.conf}} file to the FILES section in {{ic|/etc/mkinitcpio.conf}} (if you have not done so already) and rebuild the initramfs once you have blacklisted the modules, and to reboot afterwards. |
− | ===Using files in /etc/modprobe.d/=== | + | === Using files in /etc/modprobe.d/ === |
Create a {{ic|.conf}} file inside {{ic|/etc/modprobe.d/}} and append a line for each module you want to blacklist, using the {{ic|blacklist}} keyword. If for example you want to prevent the {{ic|pcspkr}} module from loading: | Create a {{ic|.conf}} file inside {{ic|/etc/modprobe.d/}} and append a line for each module you want to blacklist, using the {{ic|blacklist}} keyword. If for example you want to prevent the {{ic|pcspkr}} module from loading: | ||
− | {{hc|/etc/modprobe.d/nobeep.conf| | + | {{hc|/etc/modprobe.d/nobeep.conf| |
− | blacklist pcspkr | + | #Do not load the 'pcspkr' module on boot. |
+ | |||
+ | blacklist pcspkr}} | ||
{{Note|The {{ic|blacklist}} command will blacklist a module so that it will not be loaded automatically, but the module may be loaded if another non-blacklisted module depends on it or if it is loaded manually. | {{Note|The {{ic|blacklist}} command will blacklist a module so that it will not be loaded automatically, but the module may be loaded if another non-blacklisted module depends on it or if it is loaded manually. | ||
Line 102: | Line 141: | ||
However, there is a workaround for this behaviour; the {{ic|install}} command instructs modprobe to run a custom command instead of inserting the module in the kernel as normal, so you can force the module to always fail loading with: | However, there is a workaround for this behaviour; the {{ic|install}} command instructs modprobe to run a custom command instead of inserting the module in the kernel as normal, so you can force the module to always fail loading with: | ||
− | {{hc|/etc/modprobe.d/blacklist.conf| | + | {{hc|/etc/modprobe.d/blacklist.conf| |
− | install | + | ... |
− | ... | + | install ''module_name'' /bin/false |
+ | ...}} | ||
+ | |||
+ | This will effectively blacklist that module and any other that depends on it.}} | ||
+ | |||
+ | === Using kernel command line === | ||
+ | |||
+ | {{Tip|This can be very useful if a broken module makes it impossible to boot your system.}} | ||
+ | |||
+ | You can also blacklist modules from the bootloader. | ||
+ | |||
+ | Simply add {{ic|1=modprobe.blacklist=modname1,modname2,modname3}} to your bootloader's kernel line, as described in [[Kernel_parameters#When_starting_the_kernel|Kernel Parameters]]. | ||
+ | |||
+ | {{Note|When you are blacklisting more than one module, note that they are separated by commas only. Spaces or anything else might presumably break the syntax.}} | ||
− | + | == Tips and tricks == | |
− | === | + | === Bash function to list module parameters === |
− | {{ | + | Here is a nice bash function to be run as root that will show a list of all the currently loaded modules and all of their parameters, including the current value of the parameter. It uses {{ic|/proc/modules}} to retrieve the current list of loaded modules, then access the module file directly with modinfo to grab a description of the module and descriptions for each param (if available), finally it accesses the sysfs filesystem to grab the actual parameter names and currently loaded values. |
− | + | {{bc|<nowiki> | |
− | + | function aa_mod_parameters () | |
+ | { | ||
+ | N=/dev/null; | ||
+ | C=`tput op` O=$(echo -en "\n`tput setaf 2`>>> `tput op`"); | ||
+ | for mod in $(cat /proc/modules|cut -d" " -f1); | ||
+ | do | ||
+ | md=/sys/module/$mod/parameters; | ||
+ | [[ ! -d $md ]] && continue; | ||
+ | m=$mod; | ||
+ | d=`modinfo -d $m 2>$N | tr "\n" "\t"`; | ||
+ | echo -en "$O$m$C"; | ||
+ | [[ ${#d} -gt 0 ]] && echo -n " - $d"; | ||
+ | echo; | ||
+ | for mc in $(cd $md; echo *); | ||
+ | do | ||
+ | de=`modinfo -p $mod 2>$N | grep ^$mc 2>$N|sed "s/^$mc=//" 2>$N`; | ||
+ | echo -en "\t$mc=`cat $md/$mc 2>$N`"; | ||
+ | [[ ${#de} -gt 1 ]] && echo -en " - $de"; | ||
+ | echo; | ||
+ | done; | ||
+ | done | ||
+ | }</nowiki>}} | ||
− | + | Here is some sample output: | |
− | + | {{hc|# aa_mod_parameters|2= | |
+ | >>> ehci_hcd - USB 2.0 'Enhanced' Host Controller (EHCI) Driver | ||
+ | hird=0 - hird:host initiated resume duration, +1 for each 75us (int) | ||
+ | ignore_oc=N - ignore_oc:ignore bogus hardware overcurrent indications (bool) | ||
+ | log2_irq_thresh=0 - log2_irq_thresh:log2 IRQ latency, 1-64 microframes (int) | ||
+ | park=0 - park:park setting; 1-3 back-to-back async packets (uint) | ||
− | === | + | >>> processor - ACPI Processor Driver |
+ | ignore_ppc=-1 - ignore_ppc:If the frequency of your machine gets wronglylimited by BIOS, this should help (int) | ||
+ | ignore_tpc=0 - ignore_tpc:Disable broken BIOS _TPC throttling support (int) | ||
+ | latency_factor=2 - latency_factor: (uint) | ||
− | + | >>> usb_storage - USB Mass Storage driver for Linux | |
− | + | delay_use=1 - delay_use:seconds to delay before using a new device (uint) | |
− | + | option_zero_cd=1 - option_zero_cd:ZeroCD mode (1=Force Modem (default), 2=Allow CD-Rom (uint) | |
+ | quirks= - quirks:supplemental list of device IDs and their quirks (string) | ||
+ | swi_tru_install=1 - swi_tru_install:TRU-Install mode (1=Full Logic (def), 2=Force CD-Rom, 3=Force Modem) (uint) | ||
− | + | >>> video - ACPI Video Driver | |
− | + | allow_duplicates=N - allow_duplicates: (bool) | |
− | + | brightness_switch_enabled=Y - brightness_switch_enabled: (bool) | |
+ | use_bios_initial_backlight=Y - use_bios_initial_backlight: (bool)}} | ||
− | ==See also== | + | == See also == |
− | |||
− | |||
*[[Disable PC Speaker Beep]] | *[[Disable PC Speaker Beep]] |
Revision as of 19:37, 26 March 2013
zh-CN:Kernel modules Template:Article summary start Template:Article summary text Template:Article summary heading Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary heading Template:Article summary link Template:Article summary end
Kernel modules are pieces of code that can be loaded and unloaded into the kernel upon demand. They extend the functionality of the kernel without the need to reboot the system.
Contents
Overview
To create a kernel module, you can read this guide. A module can be configured to be build-in or loadable. To dynamically load or remove a module, it has to be configured as a loadable module in the kernel configuration (the line related to the module will therefore display the letter M
).
Modules are stored in /usr/lib/modules/kernel_release
. You can use the command uname -r
to get your current kernel release version.
_
) or dashes (-
), however those symbols are interchangeable both when using the modprobe
command and in configuration files in /etc/modprobe.d/
.Obtaining information
To show what kernel modules are currently loaded:
$ lsmod
To show information about a module:
$ modinfo module_name
To list the options that are set for a loaded module:
$ systool -v -m module_name
To display the comprehensive configuration of all the modules:
$ modprobe -c | less
To display the configuration of a particular module:
$ modprobe -c | grep module_name
List the dependencies of a module (or alias), including the module itself:
$ modprobe --show-depends module_name
Loading
The /sbin/modprobe
command handles the addition and removal of modules from the Linux kernel.
To manually load (or add) a module, run:
# modprobe module_name
Most modules should be loaded on-demand. Modules to be unconditionally loaded at boot can be specified in /etc/modules-load.d/
, for example:
/etc/modules-load.d/virtio-net.conf
#Load 'virtio-net.ko' at boot. virtio-net
Removal
To remove (or unload) a module, use the following command:
# modprobe -r module_name
Or, alternatively:
# rmmod module_name
Configuration
To pass a parameter to a kernel module you can use a modprobe conf file or use the kernel command line. See also Systemd#Kernel_modules.
Using files in /etc/modprobe.d/
The /etc/modprobe.d/
directory can be used to pass module settings to udev, which will use modprobe
to manage the loading of the modules during system boot. You can use configuration files with any name in the directory, given that they end with the .conf
extension. The syntax is:
/etc/modprobe.d/myfilename.conf
options modname parametername=parametercontents
For example:
/etc/modprobe.d/thinkfan.conf
#On Thinkpads, this lets the 'thinkfan' daemon control fan speed. options thinkpad_acpi fan_control=1
.conf
-file to FILES in mkinitcpio.conf.Using kernel command line
If the module is built into the kernel you can also pass options to the module using the kernel command line. For all common Bootloaders the following syntax is correct:
modname.parametername=parametercontents
for example:
thinkpad_acpi.fan_control=1
Simply add this to your bootloaders kernel-line as described in Kernel Parameters.
Aliasing
Aliases are alternate names for a module. For example: "alias my-mod really_long_modulename" means you can use "modprobe my-mod" instead of "modprobe really_long_modulename". You can also use shell-style wildcards, so "alias my-mod* really_long_modulename" means that "modprobe my-mod-something" has the same effect. Create an alias:
/etc/modprobe.d/myalias.conf
alias mymod really_long_module_name
Some modules have aliases which are used to autoload them when they are needed by an application. Disabling these aliases can prevent auto-loading, but will still allow the modules to be manually loaded.
/etc/modprobe.d/modprobe.conf
#Prevent Bluetooth autoload. alias net-pf-31 off
Blacklisting
Blacklisting, in the context of kernel modules, is a mechanism to prevent the kernel module from loading. This could be useful if, for example, the associated hardware is not needed, or if loading that module causes problems: for instance there may be two kernel modules that try to control the same piece of hardware, and loading them together would result in a conflict.
Some modules are loaded as part of the initramfs. mkinitcpio -M
will print out all autodetected modules: to prevent the initramfs from loading some of those modules, blacklist them in /etc/modprobe.d/modprobe.conf
. Running mkinitcpio -v
will list all modules pulled in by the various hooks (e.g. filesystem hook, SCSI hook, etc.). Remember to add that .conf
file to the FILES section in /etc/mkinitcpio.conf
(if you have not done so already) and rebuild the initramfs once you have blacklisted the modules, and to reboot afterwards.
Using files in /etc/modprobe.d/
Create a .conf
file inside /etc/modprobe.d/
and append a line for each module you want to blacklist, using the blacklist
keyword. If for example you want to prevent the pcspkr
module from loading:
/etc/modprobe.d/nobeep.conf
#Do not load the 'pcspkr' module on boot. blacklist pcspkr
blacklist
command will blacklist a module so that it will not be loaded automatically, but the module may be loaded if another non-blacklisted module depends on it or if it is loaded manually.
However, there is a workaround for this behaviour; the install
command instructs modprobe to run a custom command instead of inserting the module in the kernel as normal, so you can force the module to always fail loading with:
/etc/modprobe.d/blacklist.conf
... install module_name /bin/false ...This will effectively blacklist that module and any other that depends on it.
Using kernel command line
You can also blacklist modules from the bootloader.
Simply add modprobe.blacklist=modname1,modname2,modname3
to your bootloader's kernel line, as described in Kernel Parameters.
Tips and tricks
Bash function to list module parameters
Here is a nice bash function to be run as root that will show a list of all the currently loaded modules and all of their parameters, including the current value of the parameter. It uses /proc/modules
to retrieve the current list of loaded modules, then access the module file directly with modinfo to grab a description of the module and descriptions for each param (if available), finally it accesses the sysfs filesystem to grab the actual parameter names and currently loaded values.
function aa_mod_parameters () { N=/dev/null; C=`tput op` O=$(echo -en "\n`tput setaf 2`>>> `tput op`"); for mod in $(cat /proc/modules|cut -d" " -f1); do md=/sys/module/$mod/parameters; [[ ! -d $md ]] && continue; m=$mod; d=`modinfo -d $m 2>$N | tr "\n" "\t"`; echo -en "$O$m$C"; [[ ${#d} -gt 0 ]] && echo -n " - $d"; echo; for mc in $(cd $md; echo *); do de=`modinfo -p $mod 2>$N | grep ^$mc 2>$N|sed "s/^$mc=//" 2>$N`; echo -en "\t$mc=`cat $md/$mc 2>$N`"; [[ ${#de} -gt 1 ]] && echo -en " - $de"; echo; done; done }
Here is some sample output:
# aa_mod_parameters
>>> ehci_hcd - USB 2.0 'Enhanced' Host Controller (EHCI) Driver hird=0 - hird:host initiated resume duration, +1 for each 75us (int) ignore_oc=N - ignore_oc:ignore bogus hardware overcurrent indications (bool) log2_irq_thresh=0 - log2_irq_thresh:log2 IRQ latency, 1-64 microframes (int) park=0 - park:park setting; 1-3 back-to-back async packets (uint) >>> processor - ACPI Processor Driver ignore_ppc=-1 - ignore_ppc:If the frequency of your machine gets wronglylimited by BIOS, this should help (int) ignore_tpc=0 - ignore_tpc:Disable broken BIOS _TPC throttling support (int) latency_factor=2 - latency_factor: (uint) >>> usb_storage - USB Mass Storage driver for Linux delay_use=1 - delay_use:seconds to delay before using a new device (uint) option_zero_cd=1 - option_zero_cd:ZeroCD mode (1=Force Modem (default), 2=Allow CD-Rom (uint) quirks= - quirks:supplemental list of device IDs and their quirks (string) swi_tru_install=1 - swi_tru_install:TRU-Install mode (1=Full Logic (def), 2=Force CD-Rom, 3=Force Modem) (uint) >>> video - ACPI Video Driver allow_duplicates=N - allow_duplicates: (bool) brightness_switch_enabled=Y - brightness_switch_enabled: (bool) use_bios_initial_backlight=Y - use_bios_initial_backlight: (bool)