▁reason ably ▁possible , ▁moving ▁larger ▁programs ▁and ▁rapidly ▁changing ▁data ▁to ▁other , ▁optional ▁parts ▁of ▁the ▁system . ▁This ▁increases ▁the ▁lik elihood ▁that ▁the ▁system ▁can ▁be ▁brought ▁to ▁a ▁semi - usable ▁state ▁in ▁the ▁case ▁of ▁a ▁partial ▁system ▁failure . ▁It ▁also ▁means ▁that ▁the ▁super user ▁account , ▁necessary ▁for ▁repair ing ▁a ▁broken ▁system , ▁should ▁not ▁depend ▁on ▁any ▁programs ▁outside ▁of ▁this ▁small ▁core . ▁ ▁To ▁this ▁end , ▁the ▁root ▁account ▁is ▁often ▁configured ▁with ▁a ▁shell ▁which ▁is ▁small , ▁efficient , ▁and ▁depend able , ▁but ▁awk ward ▁for ▁daily ▁use . ▁ ▁The ▁to or ▁account ▁is ▁intended ▁as ▁a ▁solution ▁to ▁this ▁problem . ▁It ▁is ▁identical ▁to ▁root , ▁but ▁is ▁configured ▁to ▁use ▁a ▁different , ▁more ▁feature ful ▁shell . ▁ ▁Altern ately , ▁to or ▁may ▁be ▁configured ▁with ▁the ▁emer gency ▁shell , ▁allowing ▁root ▁the ▁freedom ▁to ▁use ▁the ▁feature ful ▁one . ▁ ▁Im plementation ▁In ▁a ▁Unix - like ▁system , ▁each ▁user ▁has ▁a ▁user ▁ID ▁number , ▁which ▁is ▁what ▁the ▁kernel ▁uses ▁to ▁distinguish ▁users ▁and ▁to ▁manage ▁user ▁permissions . ▁User ▁ID ▁# 0 ▁is ▁reserved ▁as ▁the ▁super user ▁account , ▁and ▁is ▁given ▁permission ▁to ▁do ▁anything ▁on ▁the ▁system . ▁ ▁Users ▁log ▁in ▁by ▁username , ▁not ▁by ▁ID ▁number , ▁and ▁a ▁user ' s ▁choice ▁of ▁login ▁shell ▁is ▁also ▁managed ▁by ▁name . ▁This ▁separation ▁between ▁name ▁and