arcstat-ui: 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/arcstat-ui - from package: arc-gui-clients

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

On Debian possible default full paths are:

/usr/bin/arcstat-ui - from package: arc-gui-clients

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

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