Question 85059 in Docker Question posted in
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Max size of string CMD that can be passed to Docker

In Docker references, I didn’t find any information about how long the string can be passed to Docker CMD.

  1. What are the limitations?
  2. What is the maximum number of characters I can pass to CMD?
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2

Answers


  1. 0

    I have done a simple test and found the limit of dockerfile line is 65535 on my CentOS 7/x64 machine.

    #./build.sh
Sending build context to Docker daemon    363kB
Error response from daemon: failed to parse Dockerfile: dockerfile line greater than max allowed size of 65535
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  2. 0

    @ZenithS You’re right for Windows (8192 Characters), but Linux is not that easy.

    To make it short: For Linux it’s hardcoded to 64 or 128 kiB. You could check with xargs --show-limits, which gives a pretty detailed overview:

    Your environment variables take up 5354 bytes
POSIX upper limit on argument length (this system): 2089750 <-- ARG_MAX
POSIX smallest allowable upper limit on argument length (all systems): 4096
Maximum length of command we could actually use: 2084396 <-- ARG_MAX - ENV
Size of command buffer we are actually using: 131072 <-- Hardcoded limit which applies actually (see below)
Maximum parallelism (--max-procs must be no greater): 2147483647

    The hardcoded limit goes to MAX_ARG_STRLEN which is set to PAGE_SIZE * 32
    https://github.com/torvalds/linux/blob/v5.16-rc7/include/uapi/linux/binfmts.h#L15

    With getconf PAGE_SIZE you can check (mostly 2048 or 4096 on modern platforms) so results to 64 or 128 kiB.

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