limit of command length

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# 1  
Old 04-18-2008
limit of command length


Can you please help me with one question?

Does rexec command have some limitation of the length of the deliveded cmd?

Thanks in advance,
# 2  
Old 04-19-2008
Probably it does, but there are many implementations, so if it is undocumented, you will have to experiment, or look at the source.

rexec is insecure and should be replaced by ssh if at all possible anyway.

Any command handled by the exec() system call needs to be less than ARG_MAX, which is a constant defined in the kernel. POSIX requires ARG_MAX to be 4,096 bytes, but on modern systems, it's usually significantly larger.

Shameless self-promotion: How long can the command line be?
This User Gave Thanks to era For This Post:
# 3  
Old 10-11-2008
Originally Posted by era
I like the method with cpp to find the macros in the headers.

There you also write:

SunOS 4.1.3 sun4c: ARG_MAX
Instead of ARG_MAX it's still NCARGS there, like in early unix variants.
However, SunOS 4 knows "sysconf(_SC_ARG_MAX)".

IRIX 5.3 IP12: ARG_MAX / 5120
The run time limit (it can be changed with "systune") usually is higher, e.g. 20480.

There are allegedly old systems with ARG_MAX set as low as 2048 or even 1024 bytes.
I don't believe there are systems after V7 with lower limits than 5120. V7 was released 1976 and is the first unix, which feels like systems we know today. (Predecessors like V4 or V6 still had 512 as limit.)
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