arcmkdir: 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/arcmkdir - from package: nordugrid-arc-client

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

On Debian possible default full paths are:

/usr/bin/arcmkdir - from package: nordugrid-arc-client

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

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