关于ulimit命令中-N 15选项功能的技术咨询

Great question! Let's unpack that mysterious -N 15: unlimited line in your ulimit -a output.

First, let's clarify what the -N flag does in ulimit:

• The -N option is used to reference resource limits by their numeric identifier instead of their human-readable name (like -n for file descriptors).
• When ulimit -a includes -N 15, it means your system has a resource limit assigned to numeric ID 15, but ulimit doesn't map that ID to a named flag in its default output.

How to find what resource ID 15 corresponds to #

To get the actual name of this resource, you have a couple of straightforward options:

1. Check system header files
   Resource limit IDs are defined in system headers like /usr/include/sys/resource.h or /usr/include/bits/resource.h. Look for RLIMIT_* constants paired with their numeric values. On most modern Linux systems, ID 15 maps to RLIMIT_RTTIME—this controls the maximum CPU time (in microseconds) that a real-time process can consume before being terminated.

2. Use the prlimit command
   The prlimit tool is a more modern alternative to ulimit that shows all resource limits with both their names and numeric IDs. Run this command to see details for your current shell process:

   prlimit --pid $$
   

   Look for the entry with ID 15—it will display the corresponding resource name and its current limit.

Why this doesn't show up in the ulimit man page #

The ulimit man page typically documents the named flags (like -t, -n, etc.), but numeric resource IDs are system-specific. The mapping between IDs and resource names is defined by your OS's kernel and C library, which is why it's not covered in the general ulimit manual.

内容的提问来源于stack exchange，提问作者Guillaume Favelier