wireshark: 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/wireshark - from package: wireshark-gnome
/usr/sbin/wireshark - from package: wireshark-gnome

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

On Debian possible default full paths are:

/usr/bin/wireshark - from package: wireshark

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

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