i2cset: 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/sbin/i2cset - from package: i2c-tools

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

On Debian possible default full paths are:

/usr/sbin/i2cset - from package: i2c-tools

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

Error in other languages:
i2cset: bevel nie gevind nie
i2cset: comandă negăsită
i2cset: comando não encontrado
i2cset: commande introuvable
i2cset: command not found
i2cset: käsku ei ole
i2cset: không tìm thấy lệnh
i2cset: komanda nerasta
i2cset: Kommando nicht gefunden.
i2cset: kommandot finns inte
i2cset: komut yok
i2cset: nie znaleziono polecenia
i2cset: níor aimsíodh an t-ordú
i2cset: no se encontró la orden
i2cset: no s'ha trobat l'ordre
i2cset: opdracht niet gevonden
i2cset: parancs nem található
i2cset: perintah tidak ditemukan
i2cset: príkaz nenájdený
i2cset: příkaz nenalezen
i2cset: команда не найдена
i2cset: командата не е открита
i2cset: 命令找不到
i2cset: コマンドが見つかりません