Difference between ulimit, lsof, cat /proc/sys/fs/file-max

https://unix.stackexchange.com/questions/476351/difference-between-ulimit-lsof-cat-proc-sys-fs-file-max

https://www.cyberciti.biz/faq/linux-increase-the-maximum-number-of-open-files/

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/tuning_and_optimizing_red_hat_enterprise_linux_for_oracle_9i_and_10g_databases/chap-oracle_9i_and_10g_tuning_guide-setting_file_handles

https://serverfault.com/questions/122679/how-do-ulimit-n-and-proc-sys-fs-file-max-differ

file-max是全局约束。

ulimit -n中是对某个用户的每个进程的约束(open files)。

ulimit -aH是hard limit