Having been directed to initramfs by an answer to my earlier question (thanks!), I’ve been working on getting initramfs working. I can now boot the kernel and drop to a shell prompt, where I can execute busybox commands, which is awesome.
Here’s where I’m stuck– there are (at least) two methods of generating initramfs images:
- By passing the kernel a path to a prebuilt directory hierarchy to be compressed
- By passing the kernel the name of a file that lists the files to be included.
The second method seemed a little cleaner, so I’ve been using that.
Just for reference, here’s my file list so far:
dir /dev 755 0 0 nod /dev/console 644 0 0 c 5 1 nod /dev/loop0 644 0 0 b 7 0 dir /bin 755 1000 1000 slink /bin/sh busybox 777 0 0 file /bin/busybox /home/brandon/rascal-initramfs/bin/busybox 755 0 0 dir /proc 755 0 0 dir /sys 755 0 0 dir /mnt 755 0 0 file /init /home/brandon/rascal-initramfs/init.sh 755 0 0
Unfortunately, I have learned that busybox requires a long list of links to serve as aliases to all of its different commands. Is there a way to generate the list of all these commands so I can add it to my file list?
Alternatively, I could switch to method 1, using the prebuilt directory hierarchy, but I’m not sure how to make the /dev nodes in that case.
Both of these paths seem messy. Is there an elegant solution to this?
Answers:
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Method 1
The first few lines of the initscript in my initramfs are simply:
busybox --install -s
Creates the symlinks for you.. Only takes an unmeasurably small amount of time on my 500Mhz board, possibly longer on very low hardware, but likely manageable. Saves a bunch of issues remembering to create all the right links when you update BB…
Method 2
It’s not the kernel that’s generating the initramfs, it’s cpio. So what you’re really looking for is a way to build a cpio archive that contains devices, symbolic links, etc.
Your method 2 uses usr/gen_init_cpio in the kernel source tree to build the cpio archive during the kernel build. That’s indeed a good way of building a cpio archive without having to populate the local filesystem first (which would require being root to create all the devices, or using fakeroot or a FUSE filesystem which I’m not sure has been written already).
All you’re missing is generating the input file to gen_init_cpio as a build step. E.g. in shell:
INITRAMFS_SOURCE_DIR=/home/brandon/rascal-initramfs exec >initramfs_source.txt echo "dir /bin 755 0 0" echo "file /bin/busybox $INITRAMFS_SOURCE_DIR/bin/busybox 755 0 0" for x in sh ls cp …; do echo "slink /bin/$x busybox 777 0 0" done # etc …
If you want to reflect the symbolic links to busybox that are present in your build tree, here’s a way (I assume you’re building on Linux):
( cd "$INITRAMFS_SOURCE_DIR/bin" &&
for x in *; do
if [ "$(readlink "$x")" = busybox ]; then
echo "slink /bin/$x busybox 777 0 0"
fi
done )
Here’s a way to copy all your symbolic links:
find "$INITRAMFS_SOURCE_DIR" -type l -printf 'slink %p %l 777 0 0n'
For busybox, maybe your build tree doesn’t have the symlinks, and instead you want to create one for every utility that you’ve compiled in. The simplest way I can think of is to look through your busybox build tree for .*.o.cmd files: there’s one per generated command.
find /path/to/busybox/build/tree -name '.*.cmd' -exec sh -c '
for x; do
x=${x##*/.}
echo "slink /bin/${x%%.*} busybox 777 0 0"
done
' _ {} +
Method 3
If you are in the busybox shell (ash) you don’t need to worry about aliases as they will be run as commands by default IIRC. Anyway busybox --help gives list of supported commands. In my case they are:
% busybox --help
BusyBox v1.17.4 (2010-11-25 12:49:55 GMT) multi-call binary.
Copyright (C) 1998-2009 Erik Andersen, Rob Landley, Denys Vlasenko
and others. Licensed under GPLv2.
See source distribution for full notice.
Usage: busybox [function] [arguments]...
or: function [arguments]...
BusyBox is a multi-call binary that combines many common Unix
utilities into a single executable. Most people will create a
link to busybox for each function they wish to use and BusyBox
will act like whatever it was invoked as.
Currently defined functions:
[, [[, acpid, addgroup, adduser, adjtimex, ar, arp, arping, ash, awk,
basename, bb, bbconfig, bbsh, beep, blkid, bootchartd, brctl, bunzip2,
bzcat, bzip2, cal, cat, catv, chat, chattr, chgrp, chmod, chown,
chpasswd, chpst, chroot, chrt, chvt, cksum, clear, cmp, comm, conspy,
cp, cpio, crond, cryptpw, cttyhack, cut, date, dd, deallocvt, delgroup,
deluser, depmod, devmem, df, dhcprelay, diff, dirname, dmesg,
dnsdomainname, dos2unix, dpkg-deb, du, dumpkmap, dumpleases, echo, ed,
egrep, eject, env, envdir, envuidgid, ether-wake, expand, expr, false,
fbset, fdflush, fdformat, fdisk, fgconsole, fgrep, find, findfs,
flash_eraseall, flash_lock, flash_unlock, flashcp, flock, free,
freeramdisk, fsck, fsck.minix, fsync, ftpd, fuser, getopt, getty, grep,
gunzip, gzip, halt, hd, hdparm, head, hexdump, hostname, httpd,
hwclock, id, ifconfig, ifdown, ifenslave, ifplugd, ifup, init, insmod,
install, ionice, ip, ipaddr, ipcrm, ipcs, iplink, iproute, iprule,
iptunnel, kbd_mode, kill, killall, killall5, klogd, last, length, less,
linux32, linux64, linuxrc, ln, loadfont, loadkmap, logger, login,
logread, losetup, lpq, lpr, ls, lsattr, lsmod, lspci, lsusb, lzcat,
lzma, lzop, lzopcat, makedevs, makemime, man, md5sum, mdev, mesg,
microcom, mkdir, mkdosfs, mke2fs, mkfifo, mkfs.ext2, mkfs.minix,
mkfs.reiser, mkfs.vfat, mknod, mkpasswd, mkswap, mktemp, modinfo,
modprobe, more, mount, mountpoint, mt, mv, nameif, nc, netstat, nice,
nmeter, nohup, nslookup, ntpd, openvt, passwd, patch, pgrep, pidof,
ping, ping6, pipe_progress, pivot_root, pkill, popmaildir, poweroff,
printenv, printf, ps, pscan, pwd, raidautorun, rdate, rdev, readahead,
readlink, readprofile, realpath, reboot, reformime, renice, reset,
resize, rev, rm, rmdir, rmmod, route, rtcwake, run-parts, runlevel,
runsv, runsvdir, rx, script, scriptreplay, sed, sendmail, seq, setarch,
setconsole, setfont, setkeycodes, setlogcons, setsid, setuidgid, sh,
sha1sum, sha256sum, sha512sum, showkey, sleep, smemcap, softlimit,
sort, split, start-stop-daemon, stat, strings, stty, su, sum, sv,
svlogd, swapoff, swapon, switch_root, sync, sysctl, syslogd, tac, tail,
tar, tee, telnet, telnetd, test, tftp, tftpd, time, timeout, top,
touch, tr, traceroute, traceroute6, true, tty, ttysize, tunctl,
tune2fs, ubiattach, ubidetach, udhcpc, udhcpd, umount, uname,
uncompress, unexpand, uniq, unix2dos, unlzma, unlzop, unxz, unzip,
uptime, usleep, vconfig, vi, vlock, volname, wall, watch, watchdog, wc,
wget, which, who, whoami, xargs, xz, xzcat, yes, zcat, zcip
In case of first method you create by mknod(1) command. For example:
# mknod /my/dir/with/initrd/dev/console -m 644 c 5 0
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0