smp_write_gpio: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/smp_write_gpio - from package: smp_utils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/smp_write_gpio - from package: smp-utils

You may install the required package with command apt-get install {package}

Error in other languages:
smp_write_gpio: bevel nie gevind nie
smp_write_gpio: comandă negăsită
smp_write_gpio: comando não encontrado
smp_write_gpio: commande introuvable
smp_write_gpio: command not found
smp_write_gpio: käsku ei ole
smp_write_gpio: không tìm thấy lệnh
smp_write_gpio: komanda nerasta
smp_write_gpio: Kommando nicht gefunden.
smp_write_gpio: kommandot finns inte
smp_write_gpio: komut yok
smp_write_gpio: nie znaleziono polecenia
smp_write_gpio: níor aimsíodh an t-ordú
smp_write_gpio: no se encontró la orden
smp_write_gpio: no s'ha trobat l'ordre
smp_write_gpio: opdracht niet gevonden
smp_write_gpio: parancs nem található
smp_write_gpio: perintah tidak ditemukan
smp_write_gpio: príkaz nenájdený
smp_write_gpio: příkaz nenalezen
smp_write_gpio: команда не найдена
smp_write_gpio: командата не е открита
smp_write_gpio: 命令找不到
smp_write_gpio: コマンドが見つかりません