rsnapshot: 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/rsnapshot - from package: rsnapshot

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

On Debian possible default full paths are:

/usr/bin/rsnapshot - from package: rsnapshot

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

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