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By default, the maximum PID number is 32,767 (PID_MAX_DEFAULT - 1); the system administrator may reduce this limit by writing a smaller value into the /proc /sys/kernel/pid_max file (/proc is the mount point of a special filesystem, see the section "Special Filesystems" in Chapter 12). In 64-bit architectures, the system administrator can enlarge the maximum PID number up to 4,194,303.