{ "content": [ { "type": "text", "text": "# initramfs-tools (man)\n\n## NAME\n\ninitramfs-tools - an introduction to writing scripts for mkinitramfs\n\n## DESCRIPTION\n\ninitramfs-tools has one main script and two different sets of subscripts which will be used\nduring different phases of execution. Each of these will be discussed separately below with\nthe help of an imaginary tool which performs a frobnication of a lvm partition prior to\nmounting the root partition.\n\n## Sections\n\n- **NAME**\n- **DESCRIPTION** (3 subsections)\n- **SCRIPTS** (3 subsections)\n- **CONFIGURATION HOOK SCRIPTS**\n- **HOOK SCRIPTS** (6 subsections)\n- **BOOT SCRIPTS** (4 subsections)\n- **EXAMPLES** (3 subsections)\n- **UPDATING THE INITRAMFS FROM ANOTHER PACKAGE**\n- **KERNEL HOOKS**\n- **DEBUG**\n- **FILES**\n- **AUTHOR**\n- **SEE ALSO**\n\nUse structuredContent.sections for detailed options, examples, and full documentation.\n" } ], "structuredContent": { "command": "initramfs-tools", "section": "", "mode": "man", "summary": "initramfs-tools - an introduction to writing scripts for mkinitramfs", "synopsis": null, "tldr_summary": null, "tldr_examples": [], "tldr_source": null, "flags": [], "examples": [ "An example hook script would look something like this (and would usually be placed in", "/etc/initramfs-tools/hooks/frobnicate):", "#!/bin/sh", "# Example frobnication hook script", "PREREQ=\"lvm\"", "prereqs()", "echo \"$PREREQ\"", "case $1 in", "prereqs)", "prereqs", "exit 0", ";;", "esac", ". /usr/share/initramfs-tools/hook-functions", "# Begin real processing below this line", "if [ ! -x \"/sbin/frobnicate\" ]; then", "exit 0", "fi", "forceload frobnicator interval=10", "copyexec /sbin/frobnicate /sbin", "exit 0", "An example boot script would look something like this (and would usually be placed in", "/etc/initramfs-tools/scripts/local-top/frobnicate):", "#!/bin/sh", "# Example frobnication boot script", "PREREQ=\"lvm\"", "prereqs()", "echo \"$PREREQ\"", "case $1 in", "prereqs)", "prereqs", "exit 0", ";;", "esac", ". /scripts/functions", "# Begin real processing below this line", "if [ ! -x \"/sbin/frobnicate\" ]; then", "panic \"Frobnication executable not found\"", "fi", "if [ ! -e \"/dev/mapper/frobb\" ]; then", "panic \"Frobnication device not found\"", "fi", "logbeginmsg \"Starting frobnication\"", "/sbin/frobnicate \"/dev/mapper/frobb\" || panic \"Frobnication failed\"", "logendmsg", "exit 0", "init sets several variables for the boot scripts environment.", "ROOT corresponds to the root boot option. Advanced boot scripts like cryptsetup or live-", "initramfs need to play tricks. Otherwise keep it alone.", "ROOTDELAY, ROOTFLAGS, ROOTFSTYPE, IP", "corresponds to the rootdelay, rootflags, rootfstype or ip boot option. Use of ROOTDE‐", "LAY is deprecated; you should implement a local-block boot script rather than delaying", "or polling.", "DPKGARCH", "allows arch specific boot actions.", "blacklist, panic, quiet, resume, noresume, resumeoffset", "set according relevant boot option.", "break Useful for manual intervention during setup and coding an boot script.", "REASON", "Argument passed to the panic helper function. Use to find out why you landed in the", "initramfs shell.", "init passes the path to init(8) usually /sbin/init.", "readonly", "is the default for mounting the root corresponds to the ro bootarg. Overridden by rw", "bootarg.", "rootmnt", "is the path where root gets mounted usually /root.", "debug indicates that a debug log is captured for further investigation." ], "see_also": [ { "name": "initramfs.conf", "section": "5", "url": "https://www.chedong.com/phpMan.php/man/initramfs.conf/5/json" }, { "name": "mkinitramfs", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/mkinitramfs/8/json" }, { "name": "update-initramfs", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/update-initramfs/8/json" }, { "name": "lsinitramfs", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/lsinitramfs/8/json" }, { "name": "INITRAMFS-TOOLS", "section": "7", "url": "https://www.chedong.com/phpMan.php/man/INITRAMFS-TOOLS/7/json" } ], "section_outline": [ { "name": "NAME", "lines": 3, "subsections": [] }, { "name": "DESCRIPTION", "lines": 6, "subsections": [ { "name": "Kernel Command Line", "lines": 7 }, { "name": "Standard", "lines": 101 }, { "name": "Debug", "lines": 26 } ] }, { "name": "SCRIPTS", "lines": 4, "subsections": [ { "name": "Configuration hook scripts", "lines": 4 }, { "name": "Hook scripts", "lines": 5 }, { "name": "Boot scripts", "lines": 5 } ] }, { "name": "CONFIGURATION HOOK SCRIPTS", "lines": 9, "subsections": [] }, { "name": "HOOK SCRIPTS", "lines": 15, "subsections": [ { "name": "Header", "lines": 24 }, { "name": "Help functions", "lines": 30 }, { "name": "Including binaries", "lines": 10 }, { "name": "Including a system firmware preimage (early initramfs)", "lines": 4 }, { "name": "Example:", "lines": 7 }, { "name": "Exported variables", "lines": 30 } ] }, { "name": "BOOT SCRIPTS", "lines": 5, "subsections": [ { "name": "Header", "lines": 21 }, { "name": "Help functions", "lines": 42 }, { "name": "Subdirectories", "lines": 38 }, { "name": "Boot parameters", "lines": 6 } ] }, { "name": "EXAMPLES", "lines": 1, "subsections": [ { "name": "Hook script", "lines": 31 }, { "name": "Boot script", "lines": 36 }, { "name": "Exported variables", "lines": 36 } ] }, { "name": "UPDATING THE INITRAMFS FROM ANOTHER PACKAGE", "lines": 12, "subsections": [] }, { "name": "KERNEL HOOKS", "lines": 8, "subsections": [] }, { "name": "DEBUG", "lines": 6, "subsections": [] }, { "name": "FILES", "lines": 11, "subsections": [] }, { "name": "AUTHOR", "lines": 7, "subsections": [] }, { "name": "SEE ALSO", "lines": 5, "subsections": [] } ], "sections": { "NAME": { "content": "initramfs-tools - an introduction to writing scripts for mkinitramfs\n\n", "subsections": [] }, "DESCRIPTION": { "content": "initramfs-tools has one main script and two different sets of subscripts which will be used\nduring different phases of execution. Each of these will be discussed separately below with\nthe help of an imaginary tool which performs a frobnication of a lvm partition prior to\nmounting the root partition.\n\n", "subsections": [ { "name": "Kernel Command Line", "content": "The root filesystem used by the kernel is specified by the boot loader as always. The tradi‐\ntional root=/dev/sda1 style device specification is allowed. If a label is used, as in\nroot=LABEL=rootPart the initrd will search all available devices for a filesystem with the\nappropriate label, and mount that device as the root filesystem. root=UUID=uuidnumber will\nmount the partition with that UUID as the root filesystem.\n\n" }, { "name": "Standard", "content": "init= \"\"\nthe binary to hand over execution to on the root fs after the initramfs scripts are\ndone.\n\n\ninitramfs.clear\nclear screen at the beginning\n\n\ninitramfs.runsize\nThe size of the /run tmpfs mount point in bytes (suffixes are supported) or as per‐\ncentage of your physical RAM. This parameter is used as the value of the size mount\noption to tmpfs. See https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt\nfor details. The default is 10%.\n\n\nroot= \"\"\nthe device node to mount as the root file system. The recommended usage is to specify\nthe UUID as followed \"root=UUID=xxx\".\n\n\nrootfstype\nset the root file system type.\n\n\nroottimeout\nset timeout in seconds. Determines how long mountroot waits for root to appear. The\ndefault is 30 seconds.\n\n\nrootdelay\nalias for roottimeout.\n\n\nrootflags\nset the file system mount option string.\n\n\nloop= \"\"\npath within the original root file system to loop-mount and use as the real root file\nsystem.\n\n\nloopfstype\nset the loop file system type, if applicable.\n\n\nloopflags\nset the loop file system mount option string, if applicable.\n\n\nnfsroot\ncan be either \"auto\" to try to get the relevant information from DHCP or a string of\nthe form NFSSERVER:NFSPATH or NFSSERVER:NFSPATH:NFSOPTS. Use root=/dev/nfs for NFS to\nkick to in. NFSOPTS can be looked up in nfs(5).\n\n\nip tells how to configure the ip address. Allows one to specify an different NFS server\nthan the DHCP server. See Documentation/filesystems/nfsroot.txt in any recent Linux\nsource for details. Optional parameter for NFS root.\n\n\nvlan tells to create a VLAN tagged device. Allows one to configure one or multiple VLAN\ntagged devices using the \"vlan=$name.$id:$parent\" syntax. E.g. \"vlan=eth0.1:eth0\" Op‐\ntional parameter for NFS root.\n\n\nBOOTIF\nis a mac address in pxelinux format with leading \"01-\" and \"-\" as separations. px‐\nelinux passes mac address of network card used to PXE boot on with this bootarg.\n\n\nboot either local or NFS (affects which initramfs scripts are run, see the \"Subdirectories\"\nsection under boot scripts).\n\n\nresume\nThe resume hook tries to autodetect the resume partition and uses the first swap par‐\ntition as valid guess. It is possible to set the RESUME variable in /etc/initramfs-\ntools/conf.d/resume. The boot variable noresume overrides it.\n\n\nresumeoffset\nSpecify the offset from the partition given by \"resume=\" at which the swap header of\nthe swap file is located.\n\n\nquiet reduces the amount of text output to the console during boot.\n\n\nro mounts the rootfs read-only.\n\n\nrw mounts the rootfs read-write.\n\n\nblacklist\ndisables load of specific modules. Use blacklist=module1,module2,module3 bootparame‐\nter.\n\n" }, { "name": "Debug", "content": "panic sets an timeout on panic. panic= is a documented security feature: it disables\nthe debug shell.\n\n\ndebug generates lots of output. It writes a log to /run/initramfs/initramfs.debug. Instead\nwhen invoked with an arbitrary argument output is written to console. Use for example\n\"debug=vc\".\n\n\nbreak spawns a shell in the initramfs image at the chosen phase (top, modules, premount,\nmount, mountroot, bottom, init) before actually executing the corresponding scripts\n(see the \"Boot scripts\" section) or action. Multiple phases may be specified, delim‐\nited by commas. The default, if no phase is specified, is \"premount\". Beware that if\nboth \"panic\" and \"break\" are present, initramfs will not spawn any shells but reboot\ninstead.\n\n\nnetconsole\nloads netconsole linux modules with the chosen args.\n\n\nallgenericide\nloads generic IDE/ATA chipset support on boot.\n\n\n" } ] }, "SCRIPTS": { "content": "Valid boot and hook scripts names consist solely of alphabetics, numerics, dashes and under‐\nscores. Other scripts are discarded.\n\n", "subsections": [ { "name": "Configuration hook scripts", "content": "These are used to override the user configuration where necessary, for example to force use\nof busybox instead of klibc utilities.\n\n" }, { "name": "Hook scripts", "content": "These are used when an initramfs image is created and not included in the image itself. They\ncan however cause files to be included in the image. Hook scripts are executed under er‐\nrexit. Thus a hook script can abort the mkinitramfs build on possible errors (exitcode != 0).\n\n" }, { "name": "Boot scripts", "content": "These are included in the initramfs image and normally executed during kernel boot in the\nearly user-space before the root partition has been mounted.\n\n\n" } ] }, "CONFIGURATION HOOK SCRIPTS": { "content": "Configuration hook scripts can be found in /usr/share/initramfs-tools/conf-hooks.d. They are\nsourced by mkinitramfs after the configuration files in /etc and before running any hook\nscripts. They can override any of the variables documented in initramfs.conf(5), but this\nshould be done only if absolutely necessary. For example, if a package's boot script re‐\nquires commands not provided by klibc-utils, it should also install a configuration hook that\nsets BUSYBOX=y.\n\n\n", "subsections": [] }, "HOOK SCRIPTS": { "content": "Hooks can be found in two places: /usr/share/initramfs-tools/hooks and /etc/initramfs-\ntools/hooks. They are executed during generation of the initramfs-image and are responsible\nfor including all the necessary components in the image itself. No guarantees are made as to\nthe order in which the different scripts are executed unless the prereqs are setup in the\nscript. Please notice that PREREQ is only honored inside a single directory. So first the\nscripts in /usr/share/initramfs-tools are ordered according to their PREREQ values and exe‐\ncuted. Then all scripts in /etc/initramfs-tools are ordered according to their PREREQ values\nand executed. This mean that currently there is no possibility to have a local script\n(/etc/initramfs-tools) get executed before one from the package (/usr/share/initramfs-tools).\n\nIf a hook script requires configuration beyond the exported variables listed below, it should\nread a private configuration file that is separate from the /etc/initramfs-tools directory.\nIt must not read initramfs-tools configuration files directly.\n\n", "subsections": [ { "name": "Header", "content": "In order to support prereqs, each script should begin with the following lines:\n\n#!/bin/sh\nPREREQ=\"\"\nprereqs()\n{\necho \"$PREREQ\"\n}\n\ncase $1 in\nprereqs)\nprereqs\nexit 0\n;;\nesac\n\n. /usr/share/initramfs-tools/hook-functions\n# Begin real processing below this line\n\nFor example, if you are writing a new hook script which relies on lvm, the line starting with\nPREREQ should be changed to PREREQ=\"lvm\" which will ensure that the lvm hook script is run\nbefore your custom script.\n\n" }, { "name": "Help functions", "content": "/usr/share/initramfs-tools/hook-functions contains a number of functions which deal with some\ncommon tasks in a hook script:\n\nmanualaddmodules adds a module (and any modules which it depends on) to the\ninitramfs image.\n\nExample: manualaddmodules isofs\n\n\naddmodulesfromfile reads a file containing a list of modules (one per line) to be\nadded to the initramfs image. The file can contain comments (lines starting with #)\nand arguments to the modules by writing the arguments on the same line as the name of\nthe module.\n\nExample: addmodulesfromfile /tmp/modlist\n\n\nforceload adds a module (and its dependencies) to the initramfs image and also uncon‐\nditionally loads the module during boot. Also supports passing arguments to the module\nby listing them after the module name.\n\nExample: forceload cdrom debug=1\n\n\ncopymodulesdir copies an entire module directory from /lib/modules/KERNELVERSION/\ninto the initramfs image.\n\nExample: copymodulesdir kernel/drivers/ata\n\n" }, { "name": "Including binaries", "content": "If you need to copy an executable or shared library to the initramfs module, use a command\nlike this:\n\ncopyexec /sbin/mdadm /sbin\n\nmkinitramfs will automatically detect which libraries it depends on and copy them to the\ninitramfs. This means that most executables, unless compiled with klibc, will automatically\ninclude glibc in the image which will increase its size by several hundred kilobytes.\n\n" }, { "name": "Including a system firmware preimage (early initramfs)", "content": "If you need to prepend data to the initramfs image, you need to prepare it in a file, and\ncall the prependearlyinitramfs function. The file can be disposed of as soon as the func‐\ntion returns.\n" }, { "name": "Example:", "content": "TEMPFILE=$(mktemp ...)\n...\nprependearlyinitramfs ${TEMPFILE}\nrm -f ${TEMPFILE}\n\n\n" }, { "name": "Exported variables", "content": "mkinitramfs sets several variables for the hook scripts environment.\n\n\nMODULESDIR\ncorresponds to the linux modules dir.\n\nversion\nis the $(uname -r) linux version against mkinitramfs is run.\n\nCONFDIR\nis the path of the used initramfs-tools configurations.\n\nDESTDIR\nis the root path of the newly build initramfs.\n\nDPKGARCH\nallows arch specific hook additions.\n\nverbose\ncorresponds to the verbosity of the update-initramfs run.\n\nBUSYBOX, MODULES\nare as described in initramfs.conf(5).\n\nBUSYBOXDIR\nis the directory where busybox utilities should be installed from, or empty if busybox\nis not being used.\n\n\n" } ] }, "BOOT SCRIPTS": { "content": "Similarly to hook scripts, boot scripts can be found in two places /usr/share/initramfs-\ntools/scripts/ and /etc/initramfs-tools/scripts/. There are a number of subdirectories to\nthese two directories which control the boot stage at which the scripts are executed.\n\n", "subsections": [ { "name": "Header", "content": "Like for hook scripts, there are no guarantees as to the order in which the different scripts\nin one subdirectory (see \"Subdirectories\" below) are executed. In order to define a certain\norder, a similar header as for hook scripts should be used:\n\n#!/bin/sh\nPREREQ=\"\"\nprereqs()\n{\necho \"$PREREQ\"\n}\n\ncase $1 in\nprereqs)\nprereqs\nexit 0\n;;\nesac\n\nWhere PREREQ is modified to list other scripts in the same subdirectory if necessary.\n\n" }, { "name": "Help functions", "content": "A number of functions (mostly dealing with output) are provided to boot scripts in\n/scripts/functions :\n\n\nlogsuccessmsg Logs a success message\n\nExample: logsuccessmsg \"Frobnication successful\"\n\n\nlogfailuremsg Logs a failure message\n\nExample: logfailuremsg \"Frobnication component froobz missing\"\n\n\nlogwarningmsg Logs a warning message\n\nExample: logwarningmsg \"Only partial frobnication possible\"\n\n\nlogbeginmsg Logs a message that some processing step has begun\n\n\nlogendmsg Logs a message that some processing step is finished\n\nExample:\n\nlogbeginmsg \"Frobnication begun\"\n# Do something\nlogendmsg\n\n\npanic Logs an error message and executes a shell in the initramfs image to allow the\nuser to investigate the situation.\n\nExample: panic \"Frobnication failed\"\n\n\naddmountrootfailhook NN-name Deprecated: This function is now a stub which is ef‐\nfectively a no-op. It will be removed in a future version; please remove mountroot\nfailure hooks from existing packages accordingly.\n\n" }, { "name": "Subdirectories", "content": "Both /usr/share/initramfs-tools/scripts and /etc/initramfs-tools/scripts contains the follow‐\ning subdirectories.\n\n\ninit-top the scripts in this directory are the first scripts to be executed after\nsysfs and procfs have been mounted. It also runs the udev hook for populating the\n/dev tree (udev will keep running until init-bottom).\n\n\ninit-premount happens after modules specified by hooks and /etc/initramfs-tools/mod‐\nules have been loaded.\n\n\nlocal-top OR nfs-top After these scripts have been executed, the root device node is\nexpected to be present (local) or the network interface is expected to be usable\n(NFS).\n\n\nlocal-block These scripts are called with the name of a local block device. After\nthese scripts have been executed, that device node should be present. If the local-\ntop or local-block scripts fail to create the wanted device node, the local-block\nscripts will be called periodically to try again.\n\n\nlocal-premount OR nfs-premount are run after the sanity of the root device has been\nverified (local) or the network interface has been brought up (NFS), but before the\nactual root fs has been mounted.\n\n\nlocal-bottom OR nfs-bottom are run after the rootfs has been mounted (local) or the\nNFS root share has been mounted.\n\n\ninit-bottom are the last scripts to be executed before procfs and sysfs are moved to\nthe real rootfs and execution is turned over to the init binary which should now be\nfound in the mounted rootfs. udev is stopped.\n\n" }, { "name": "Boot parameters", "content": "/conf/param.conf allows boot scripts to change exported variables that are listed on\ntop of init. Write the new values to it. It will be sourced after an boot script run\nif it exists.\n\n\n" } ] }, "EXAMPLES": { "content": "", "subsections": [ { "name": "Hook script", "content": "An example hook script would look something like this (and would usually be placed in\n/etc/initramfs-tools/hooks/frobnicate):\n\n#!/bin/sh\n# Example frobnication hook script\n\nPREREQ=\"lvm\"\nprereqs()\n{\necho \"$PREREQ\"\n}\n\ncase $1 in\nprereqs)\nprereqs\nexit 0\n;;\nesac\n\n. /usr/share/initramfs-tools/hook-functions\n# Begin real processing below this line\n\nif [ ! -x \"/sbin/frobnicate\" ]; then\nexit 0\nfi\n\nforceload frobnicator interval=10\ncopyexec /sbin/frobnicate /sbin\nexit 0\n\n" }, { "name": "Boot script", "content": "An example boot script would look something like this (and would usually be placed in\n/etc/initramfs-tools/scripts/local-top/frobnicate):\n\n#!/bin/sh\n# Example frobnication boot script\n\nPREREQ=\"lvm\"\nprereqs()\n{\necho \"$PREREQ\"\n}\n\ncase $1 in\nprereqs)\nprereqs\nexit 0\n;;\nesac\n\n. /scripts/functions\n# Begin real processing below this line\nif [ ! -x \"/sbin/frobnicate\" ]; then\npanic \"Frobnication executable not found\"\nfi\n\nif [ ! -e \"/dev/mapper/frobb\" ]; then\npanic \"Frobnication device not found\"\nfi\n\nlogbeginmsg \"Starting frobnication\"\n/sbin/frobnicate \"/dev/mapper/frobb\" || panic \"Frobnication failed\"\nlogendmsg\n\nexit 0\n\n" }, { "name": "Exported variables", "content": "init sets several variables for the boot scripts environment.\n\n\nROOT corresponds to the root boot option. Advanced boot scripts like cryptsetup or live-\ninitramfs need to play tricks. Otherwise keep it alone.\n\nROOTDELAY, ROOTFLAGS, ROOTFSTYPE, IP\ncorresponds to the rootdelay, rootflags, rootfstype or ip boot option. Use of ROOTDE‐\nLAY is deprecated; you should implement a local-block boot script rather than delaying\nor polling.\n\nDPKGARCH\nallows arch specific boot actions.\n\nblacklist, panic, quiet, resume, noresume, resumeoffset\nset according relevant boot option.\n\nbreak Useful for manual intervention during setup and coding an boot script.\n\nREASON\nArgument passed to the panic helper function. Use to find out why you landed in the\ninitramfs shell.\n\ninit passes the path to init(8) usually /sbin/init.\n\nreadonly\nis the default for mounting the root corresponds to the ro bootarg. Overridden by rw\nbootarg.\n\nrootmnt\nis the path where root gets mounted usually /root.\n\ndebug indicates that a debug log is captured for further investigation.\n\n\n" } ] }, "UPDATING THE INITRAMFS FROM ANOTHER PACKAGE": { "content": "Package maintainer scripts should not run update-initramfs directly. A package that installs\nhooks for initramfs-tools should include a triggers file containing:\nactivate-noawait update-initramfs\n\nKernel packages must call the kernel hooks as documented in the Debian Kernel Handbook.\n\nA package that requires an initramfs to function, but is not a kernel package, should include\na triggers file containing:\nactivate-await update-initramfs\n\n\n", "subsections": [] }, "KERNEL HOOKS": { "content": "initramfs-tools includes hook scripts that are called by kernel packages on installation and\nremoval, so that an initramfs is automatically created, updated or deleted as necessary. The\nhook scripts do nothing if the environment variable INITRD is set to No. This will be the\ncase for kernel packages built with make deb-pkg and with CONFIGBLKDEVINITRD not set in\nthe kernel config, or built with make-kpkg and not using the --initrd option.\n\n\n", "subsections": [] }, "DEBUG": { "content": "It is easy to check the generated initramfs for its content. One may need to double-check if\nit contains the relevant binaries, libs or modules:\nlsinitramfs /boot/initrd.img-3.16-3-amd64\n\n\n", "subsections": [] }, "FILES": { "content": "/run/initramfs/fsck.log\nLog of fsck commands run within the initramfs, with their output.\n\n/run/initramfs/fsck-root\nExists only if fsck ran successfully for the root filesystem.\n\n/run/initramfs/fsck-usr\nExists only if fsck ran successfully for the /usr filesystem.\n\n\n", "subsections": [] }, "AUTHOR": { "content": "The initramfs-tools are written by Maximilian Attems , Jeff Bailey and numerous others.\n\nThis manual was written by David Härdeman , updated by Maximilian Attems\n.\n\n", "subsections": [] }, "SEE ALSO": { "content": "initramfs.conf(5), mkinitramfs(8), update-initramfs(8), lsinitramfs(8).\n\n\n\ninitramfs-tools 2018/07/18 INITRAMFS-TOOLS(7)", "subsections": [] } } } }