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?

CodePudding user response：

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

CodePudding user response：

@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.