How long can $DISPLAY environment variable value be?

Abhishek Jain

5/6/23, 5:22 AM

What is the maximum length that $DISPLAY environment variable value can take?

I understand that it is - hostname:displaynumber.screennumber

So will it be => max($DISPLAY) = max(hostname) + max (displaynumber) + max(screennumber)?

What is max length of hostname, displaynumber and screennumber on Linux?

0 + 0

environment-variables

linux-headers

cocomac

5/6/23, 5:31 AM

You have asked four different questions. I don't know about the hostname, but you almost certainly won't run into any issues with the DISPLAY variable being too long. There is probobly a limit, but you won't hit it with normal use.

Abhishek Jain

5/6/23, 5:49 AM

I understand that. I need to know the limit though as I will be persisting this information. I cannot assign something too big (as I have limited space) and i cannot assign something too less that it does not gets captured completely in some cases.

Score:2

Ubuntu

matigo

5/6/23, 5:44 AM

Environment variable length is controlled by MAX_ARG_STRLEN, which is a constant value defined as PAGE_SIZE*32 within the Linux kernel.

You can check your PAGE_SIZE value via Terminal like this:

getconf PAGE_SIZE

If you are running stock Ubuntu (or an official flavour), then the value will likely be 4096 (bytes).

So, with this in mind:

4096 * 32 = 131,072

As a result, the maximum length of an environment variable, be it $DISPLAY or any other, is 128KB. This works out to 131,072 single-byte ASCII characters.

0 + 0

Abhishek Jain

5/6/23, 7:40 AM

Thanks @matigo. This is too big and potentially defines the length in general for all environment variable. I am interested particularly in $DISPLAY environment variable. How big can it get?

matigo

5/6/23, 8:22 AM

I suggest re-reading the first seven words of the answer. *All* environment variables have the same limit. Linux is not like George Orwell's *Animal Farm*; there are no environment variables that are more equal than others

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: How long can $DISPLAY environment variable value be?

TH: ค่าตัวแปรสภาพแวดล้อม $DISPLAY สามารถอยู่ได้นานแค่ไหน?

RO: Cât de lungă poate fi valoarea variabilei de mediu $DISPLAY?

RU: Как долго может быть значение переменной окружения $DISPLAY?

VI: Giá trị biến môi trường $DISPLAY có thể kéo dài bao lâu?

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