Add /usr/sbin and /sbin to default root PATH When dropbear is used in a very restricted environment (such as in a initrd), the default user shell is often also very restricted and doesn't take care of setting the PATH so the user ends up with the PATH set by dropbear. Unfortunately, dropbear always sets "/usr/bin:/bin" as default PATH even for the root user which should have /usr/sbin and /sbin too. For a concrete instance of this problem, see the "Remote Unlocking" section in this tutorial: https://paxswill.com/blog/2013/11/04/encrypted-raspberry-pi/ It speaks of a bug in the initramfs script because it's written "blkid" instead of "/sbin/blkid"... this is just because the scripts from the initramfs do not expect to have a PATH without the sbin directories and because dropbear is not setting the PATH appropriately for the root user. I'm thus suggesting to use the attached patch to fix this misbehaviour (I did not test it, but it's easy enough). It might seem anecdotic but multiple Kali users have been bitten by this. From https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903403

#include "tommath_private.h"
#ifdef BN_MP_FROM_UBIN_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

/* reads a unsigned char array, assumes the msb is stored first [big endian] */
mp_err mp_from_ubin(mp_int *a, const unsigned char *buf, size_t size)
{
   mp_err err;

   /* make sure there are at least two digits */
   if (a->alloc < 2) {
      if ((err = mp_grow(a, 2)) != MP_OKAY) {
         return err;
      }
   }

   /* zero the int */
   mp_zero(a);

   /* read the bytes in */
   while (size-- > 0u) {
      if ((err = mp_mul_2d(a, 8, a)) != MP_OKAY) {
         return err;
      }

#ifndef MP_8BIT
      a->dp[0] |= *buf++;
      a->used += 1;
#else
      a->dp[0] = (*buf & MP_MASK);
      a->dp[1] |= ((*buf++ >> 7) & 1u);
      a->used += 2;
#endif
   }
   mp_clamp(a);
   return MP_OKAY;
}
#endif