when I want to do something: add , remove, pull , push in github, I just have this error in my terminal

Thanks in advance!

  selnaz:iOS-Tidinfo Lnaz$ git add .
  error: cannot fork() for status: Resource temporarily      unavailable
  fatal: Could not run git status --porcelain
  fatal: git status --porcelain failed
  fatal: git status --porcelain failed
  fatal: git status --porcelain failed
  fatal: git status --porcelain failed
  fatal: git status --porcelain failed
  fatal: git status --porcelain failed

Edit:

selnaz:iOS-Tidinfo Lnaz$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
file size               (blocks, -f) unlimited
max locked memory       (kbytes, -l) unlimited
max memory size         (kbytes, -m) unlimited
open files                      (-n) 256
pipe size            (512 bytes, -p) 1
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 709
virtual memory          (kbytes, -v) unlimited  

Edit2

selnaz:iOS-Tidinfo Lnaz$ ps xfu | wc -l
ps: illegal option -- f
usage: ps [-AaCcEefhjlMmrSTvwXx] [-O fmt | -o fmt] [-G gid[,gid...]]
      [-u]
      [-p pid[,pid...]] [-t tty[,tty...]] [-U user[,user...]]
   ps [-L]
   0