unlink: 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:

/bin/unlink - from package: coreutils

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

On Debian possible default full paths are:

/usr/bin/unlink - from package: coreutils

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

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