avr-gdbtui: command not found

Have You tried accessing the binary with the full path?

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/avr-gdbtui - from package: avr-gdb

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