could not create character device "foo" because you're not superuser!

[0x3h]

Windows 7 under cygwin with XZ_SUPPORT disabled. what's the cause of this ?

SquashFS version [768.256] / inode count [1912733696] suggests a SquashFS image of a different endianess Non-standard SquashFS Magic: qshs Reading a different endian SQUASHFS filesystem on mtdblock3 Parallel unsquashfs: Using 1 processor Trying to decompress using default gzip decompressor... Trying to decompress with lzma... Detected lzma compression 546 inodes (687 blocks) to write create_inode: could not create character device squashfs-root/dev/console, because you're not superuser! create_inode: could not create character device squashfs-root/dev/gpio, because you're not superuser! create_inode: could not create character device squashfs-root/dev/led, because you're not superuser! create_inode: could not create block device squashfs-root/dev/mtd, because you're not superuser! create_inode: could not create character device squashfs-root/dev/mtd0, because you're not superuser! create_inode: could not create character device squashfs-root/dev/mtd1, because you're not superuser! create_inode: could not create character device squashfs-root/dev/mtd2, because you're not superuser! create_inode: could not create character device squashfs-root/dev/mtd3, because you're not superuser! create_inode: could not create character device squashfs-root/dev/mtd4, because you're not superuser! create_inode: could not create character device squashfs-root/dev/mtd5, because you're not superuser! create_inode: could not create block device squashfs-root/dev/mtdblock0, because you're not superuser! create_inode: could not create block device squashfs-root/dev/mtdblock1, because you're not superuser! create_inode: could not create block device squashfs-root/dev/mtdblock2, because you're not superuser! create_inode: could not create block device squashfs-root/dev/mtdblock3, because you're not superuser! create_inode: could not create block device squashfs-root/dev/mtdblock4, because you're not superuser! create_inode: could not create block device squashfs-root/dev/mtdblock5, because you're not superuser! create_inode: could not create character device squashfs-root/dev/null, because you're not superuser! create_inode: could not create character device squashfs-root/dev/pmap, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ppp, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ptmx, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ptyp0, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ptyp1, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ptyp2, because you're not superuser! create_inode: could not create character device squashfs-root/dev/qostype, because you're not superuser! create_inode: could not create block device squashfs-root/dev/sda, because you're not superuser! create_inode: could not create block device squashfs-root/dev/sda1, because you're not superuser! create_inode: could not create block device squashfs-root/dev/sda2, because you're not superuser! create_inode: could not create block device squashfs-root/dev/sdb, because you're not superuser! create_inode: could not create block device squashfs-root/dev/sdb1, because you're not superuser! create_inode: could not create block device squashfs-root/dev/sdb2, because you're not superuser! create_inode: could not create character device squashfs-root/dev/tty, because you're not superuser! create_inode: could not create character device squashfs-root/dev/tty0, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ttyS0, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ttyp0, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ttyp1, because you're not superuser! create_inode: could not create character device squashfs-root/dev/ttyp2, because you're not superuser! create_inode: could not create character device squashfs-root/dev/urandom, because you're not superuser! create_inode: could not create character device squashfs-root/dev/watchdog, because you're not superuser! create_inode: could not create character device squashfs-root/dev/zero, because you're not superuser! 648/687 94% ...

[devttys0]

This is normal behavior. You need special privileges to create device files, so even when running on a Linux system as a standard user, you would get these warnings.