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# prctl() - Unix, Linux System Call

# NAME

prctl - operations on a process

# SYNOPSIS

#include <sys/prctl.h>

int prctl(int option, unsigned long arg2, unsigned long arg3 , unsigned long arg4, unsigned long arg5);

# DESCRIPTION

prctl() is called with a first argument describing what to do (with values defined in <linux/prctl.h>), and further parameters with a significance depending on the first one. The first argument can be:

Tag | Description
--- | ---
PR_SET_PDEATHSIG
| (since Linux 2.1.57) Set the parent process death signal of the current process to arg2 (either a signal value in the range 1..maxsig, or 0 to clear). This is the signal that the current process will get when its parent dies. This value is cleared upon a fork().
PR_GET_PDEATHSIG
| (since Linux 2.3.15) Read the current value of the parent process death signal into the (int *) arg2.
PR_SET_DUMPABLE
| (Since Linux 2.4) Set the state of the flag determining whether core dumps are produced for this process upon delivery of a signal whose default behaviour is to produce a core dump. (Normally this flag is set for a process by default, but it is cleared when a set-user-ID or set-group-ID program is executed and also by various system calls that manipulate process UIDs and GIDs). In kernels up to and including 2.6.12, arg2 must be either 0 (process is not dumpable) or 1 (process is dumpable). Since kernel 2.6.13, the value 2 is also permitted; this causes any binary which normally would not be dumped to be dumped readable by root only. (See also the description of /proc/sys/fs/suid_dumpable in proc(5).)
PR_GET_DUMPABLE
| (Since Linux 2.4) Return (as the function result) the current state of the calling process’s dumpable flag.
PR_SET_KEEPCAPS
| Set the state of the process’s "keep capabilities" flag, which determines whether the process’s effective and permitted capability sets are cleared when a change is made to the process’s user IDs such that the process’s real UID, effective UID, and saved set-user-ID all become non-zero when at least one of them previously had the value 0. (By default, these credential sets are cleared). arg2 must be either 0 (capabilities are cleared) or 1 (capabilities are kept).
PR_GET_KEEPCAPS
| Return (as the function result) the current state of the calling process’s "keep capabilities" flag.

# RETURN VALUE

PR_GET_DUMPABLE and PR_GET_KEEPCAPS return 0 or 1 on success. All other option values return 0 on success. On error, -1 is returned, and errno is set appropriately.

# ERRORS

Tag | Description
--- | ---
EINVAL | The value of option is not recognized, or it is PR_SET_PDEATHSIG and arg2 is not zero or a signal number.

# CONFORMING TO

This call is Linux-specific. IRIX has a prctl() system call (also introduced in Linux 2.1.44 as irix_prctl on the MIPS architecture), with prototype

ptrdiff_t prctl(int option, int arg2, int arg3);

and options to get the maximum number of processes per user, get the maximum number of processors the calling process can use, find out whether a specified process is currently blocked, get or set the maximum stack size, etc.

# AVAILABILITY

The prctl() system call was introduced in Linux 2.1.57.

# SEE ALSO

- signal (2)

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