clustal2link: 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 Debian possible default full paths are:

/usr/share/circos/tools/clustal2link/bin/clustal2link - from package: circos-tools

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

Error in other languages:
clustal2link: bevel nie gevind nie
clustal2link: comandă negăsită
clustal2link: comando não encontrado
clustal2link: commande introuvable
clustal2link: command not found
clustal2link: käsku ei ole
clustal2link: không tìm thấy lệnh
clustal2link: komanda nerasta
clustal2link: Kommando nicht gefunden.
clustal2link: kommandot finns inte
clustal2link: komut yok
clustal2link: nie znaleziono polecenia
clustal2link: níor aimsíodh an t-ordú
clustal2link: no se encontró la orden
clustal2link: no s'ha trobat l'ordre
clustal2link: opdracht niet gevonden
clustal2link: parancs nem található
clustal2link: perintah tidak ditemukan
clustal2link: príkaz nenájdený
clustal2link: příkaz nenalezen
clustal2link: команда не найдена
clustal2link: командата не е открита
clustal2link: 命令找不到
clustal2link: コマンドが見つかりません