Linux命令行参数的总长度的上限值探究

对于 Linux bash 参数过长错误 “Argument list too long” 网上有很多解决方案，但并没有解释这个最大长度的值的范围。本着追根溯源的态度，本文对此问题做一个探究。记录下限制参数长度的因素以及最大长度。

参数最大长度

如何确认Linux bash中能接受的最大长度呢？

Number of arguments and maximum length of one argument At least on Linux 2.6, there’s also a limit on the maximum number of arguments in argv[]. On Linux 2.6.14 the function do_execve() in fs/exec.c tests if the number exceeds PAGE_SIZE*MAX_ARG_PAGES-sizeof(void *) / sizeof(void *) On a 32-bit Linux, this is ARGMAX/4-1 (32767). This becomes relevant if the average length of arguments is smaller than 4. Since Linux 2.6.23, this function tests if the number exceeds MAX_ARG_STRINGS in <linux/binfmts.h> (2^32-1 = 4294967296-1). And as additional limit since 2.6.23, one argument must not be longer than MAX_ARG_STRLEN (131072). This might become relevant if you generate a long call like “sh -c ‘automatically generated with many arguments’”. (pointed out by Xan Lopez and Ralf Wildenhues)

参考ARG_MAX, maximum length of arguments for a new process 从以上文献中能看出在Linux2.6.23内核以后参数长度最长不能超过MAX_ARG_STRLEN

MAX_ARG_STRLEN在<linux/binfmts.h>中定义为:

#define MAX_ARG_STRLEN (PAGE_SIZE * 32)

验证

如下图验证所示： 可以通过getconf PAGE_SIZE 获取内存页大小。

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# 获取内存页大小
(base) [root@localhost ~]# getconf PAGE_SIZE
4096

通过echo $(( $(getconf PAGE_SIZE)*32 )) 得到 MAX_ARG_STRLEN值，

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(base) [root@localhost ~]# echo $(($(getconf PAGE_SIZE)*32))
131072

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# 131072 字节的参数列表，报错
(base) [root@localhost ~]# /bin/echo "$(printf "%*s" 131072 "a")">/dev/null
-bash: /bin/echo: Argument list too long
# 131071 字节的参数列表，没有问题
(base) [root@localhost ~]# /bin/echo "$(printf "%*s" 131071 "a")">/dev/null

131071 字节是参数列表的最大支持长度, 结果符合我们的预测。