fetchmail: 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/fetchmail - from package: fetchmail

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

On Debian possible default full paths are:

/usr/bin/fetchmail - from package: fetchmail

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

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