vmstat: 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/vmstat - from package: procps

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

On Debian possible default full paths are:

/usr/bin/vmstat - from package: procps

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

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