Shell can't find nginx
/etc/init.d/nginx is a shell script to start/stop/... the nginx service
$ file /etc/init.d/nginx/etc/init.d/nginx: POSIX shell script, ASCII text executablenginx binary is different and usually present in /usr/sbin/. Add that directory to your PATH.
$ file /usr/sbin/nginx/usr/sbin/nginx: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=c14e988f9696733869b790f49e27a488b0aff4c2, strippedOr view the file /etc/init.d/nginx to find out where nginx is installed.