Easiest way to recover Linux from root being locked out is to use Toms Root Boot. Really easy to use. All you need is the program, and access to a floppy drive on the system. Download the program at Toms Root Boot:
http://www.toms.net/rb

Included in the package:
1) tomsrtbt is

"The most GNU/Linux on one floppy disk"

for:

rescue recovery panic & emergencies

tools to keep in your shirt pockets

whenever you can't use a hard drive

Tomsrtbt stands for:

"Tom's floppy which has a root filesystem and is also bootable."
___ _ _ _ _ _

2) Design goals

as much stuff as possible on 1 floppy disk

keep it self contained, build under itself

try to make it behave like a normal system

rescue and recovery functions get priority

3) Contents

What you have is... AHA152X AHA1542 AIC7XXX BUSLOGIC DAC960 DEC_ELCP(TULIP) 
EATA EEXPRESS/PRO/PRO100 EL2 EL3 EXT2 EXT3 FAT FD IDE-CD/DISK/TAPE IMM INITRD
ISO9660 JOLIET LOOP MATH_EMULATION MINIX MSDOS NCR53C8XX NE2000 NFS NTFS
PARPORT PCINE2K PCNET32 PLIP PPA RTL8139 SD SERIAL/_CONSOLE SLIP SMC_ULTRA SR
ST VFAT VID_SELECT VORTEX WD80x3 .exrc 3c589_cs agetty ash badblocks basename
boot.b buildit.s busybox bz2bzImage bzip2 cardmgr cardmgr.pid cat chain.b
chattr chgrp chmod chown chroot clear clone.s cmp common config cp cpio cs
cut date dd dd-lfs debugfs ddate df dhcpcd-- dirname dmesg domainname ds du
dumpe2fs e2fsck echo egrep elvis ex false fdflush fdformat fdisk filesize
find findsuper fmt fstab grep group gunzip gzip halt head hexdump hexedit
host.conf hostname hosts httpd i82365 ifconfig ile init inittab insmod
install.s issue kernel key.lst kill killall killall5 ld ld-linux length
less libc libcom_err libe2p libext2fs libtermcap libuuid lilo lilo.conf ln
loadkmap login ls lsattr lsmod lua luasocket man map md5sum miterm mkdir
mkdosfs mke2fs mkfifo mkfs.minix mknod mkswap more more.help mount mt mtab mv
nc necho network networks nmclan_cs nslookup passwd pax pcmcia_core pcnet_cs
pidof ping poweroff printf profile protocols ps pwd rc.0 rc.S rc.custom
rc.custom.gz rc.pcmcia reboot rescuept reset resolv.conf rm rmdir rmmod route
rsh rshd script sed serial serial_cs services setserial settings.s sh shared
slattach sleep sln sort split stab strings swapoff swapon sync tail tar tcic
tee telnet telnetd termcap test tomshexd tomsrtbt.FAQ touch traceroute true
tune2fs umount undeb-- unpack.s unrpm-- update utmp vi vi.help view watch
wc wget which xargs xirc2ps_cs yecho yes zcat

GNU/Linux package

clone.s duplicate
fdflush flush floppy cache
fdformat format floppy 1.7M
install.s install
settings.s used by tools
tomsrtbt.FAQ documentation
tomsrtbt.raw <== This is it
unpack.s unpack for rebuild

DOS package

initrd.img installer image
install.bat install it
loadlin.exe starts GNU/Linux from DOS
tomsrtbt.FAQ documentation
zimage installer kernel

PS:
'Login as root' means the USER ID is "root"! When you load it, Toms will prompt you to enter a passwd (Toms is a filesystem on the disk which you log into as root. ) and will allow you into your system so that you can then mount the filesystem that contains the file you wish to fix (example: /etc/passwd). Search Google for Toms Root Boot and see for yourself. It will work wonders for you.

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