Are BusyBox Commands Truly Built In?
Answer : By default, BusyBox doesn't do anything special regarding the applets that it has built in (the commands listed with busybox --help ). However, if the FEATURE_SH_STANDALONE and FEATURE_PREFER_APPLETS options are enabled at compile time, then when BusyBox sh¹ executes a command which is a known applet name, it doesn't do the normal PATH lookup, but instead runs its built-in applets through a shortcut: Applets that are declared as “noexec” in the source code are executed as function calls in a forked process. As of BusyBox 1.22, the following applets are noexec: chgrp , chmod , chown , cksum , cp , cut , dd , dos2unix , env , fold , hd , head , hexdump , ln , ls , md5sum , mkfifo , mknod , sha1sum , sha256sum , sha3sum , sha512sum , sort , tac , unix2dos . Applets that are declared as “nofork” in the source code are executed as function calls in the same process. As of BusyBox 1.22, the following applets are nofork: [[ , [ , basename , cat , dirname , echo , ...