1PRCTL(2) Linux Programmer's Manual PRCTL(2)
2
6 prctl - operations on a process
7
9 #include <sys/prctl.h>
10 int prctl(int option, unsigned long arg2, unsigned long arg3,
12 unsigned long arg4, unsigned long arg5);
13
15 prctl() is called with a first argument describing what to do (with
16 values defined in <linux/prctl.h>), and further arguments with a sig‐
17 nificance depending on the first one. The first argument can be:
18 PR_CAPBSET_READ (since Linux 2.6.25)
20 Return (as the function result) 1 if the capability specified in
21 arg2 is in the calling thread's capability bounding set, or 0 if
22 it is not. (The capability constants are defined in
23 <linux/capability.h>.) The capability bounding set dictates
24 whether the process can receive the capability through a file's
25 permitted capability set on a subsequent call to execve(2).
26 If the capability specified in arg2 is not valid, then the call
28 fails with the error EINVAL.
29 PR_CAPBSET_DROP (since Linux 2.6.25)
31 If the calling thread has the CAP_SETPCAP capability, then drop
32 the capability specified by arg2 from the calling thread's capa‐
33 bility bounding set. Any children of the calling thread will
34 inherit the newly reduced bounding set.
35 The call fails with the error: EPERM if the calling thread does
37 not have the CAP_SETPCAP; EINVAL if arg2 does not represent a
38 valid capability; or EINVAL if file capabilities are not enabled
39 in the kernel, in which case bounding sets are not supported.
40 PR_SET_DUMPABLE (since Linux 2.3.20)
42 Set the state of the flag determining whether core dumps are
43 produced for this process upon delivery of a signal whose
44 default behavior is to produce a core dump. (Normally this flag
45 is set for a process by default, but it is cleared when a set-
46 user-ID or set-group-ID program is executed and also by various
47 system calls that manipulate process UIDs and GIDs). In kernels
48 up to and including 2.6.12, arg2 must be either 0 (process is
49 not dumpable) or 1 (process is dumpable). Between kernels
50 2.6.13 and 2.6.17, the value 2 was also permitted, which caused
51 any binary which normally would not be dumped to be dumped read‐
52 able by root only; for security reasons, this feature has been
53 removed. (See also the description of
54 /proc/sys/fs/suid_dumpable in proc(5).)
55 PR_GET_DUMPABLE (since Linux 2.3.20)
57 Return (as the function result) the current state of the calling
58 process's dumpable flag.
59 PR_SET_ENDIAN (since Linux 2.6.18, PowerPC only)
61 Set the endian-ness of the calling process to the value given in
62 arg2, which should be one of the following: PR_ENDIAN_BIG,
63 PR_ENDIAN_LITTLE, or PR_ENDIAN_PPC_LITTLE (PowerPC pseudo little
64 endian).
65 PR_GET_ENDIAN (since Linux 2.6.18, PowerPC only)
67 Return the endian-ness of the calling process, in the location
68 pointed to by (int *) arg2.
69 PR_SET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
71 Set floating-point emulation control bits to arg2. Pass
72 PR_FPEMU_NOPRINT to silently emulate fp operations accesses, or
73 PR_FPEMU_SIGFPE to not emulate fp operations and send SIGFPE
74 instead.
75 PR_GET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
77 Return floating-point emulation control bits, in the location
78 pointed to by (int *) arg2.
79 PR_SET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
81 Set floating-point exception mode to arg2. Pass
82 PR_FP_EXC_SW_ENABLE to use FPEXC for FP exception enables,
83 PR_FP_EXC_DIV for floating-point divide by zero, PR_FP_EXC_OVF
84 for floating-point overflow, PR_FP_EXC_UND for floating-point
85 underflow, PR_FP_EXC_RES for floating-point inexact result,
86 PR_FP_EXC_INV for floating-point invalid operation,
87 PR_FP_EXC_DISABLED for FP exceptions disabled, PR_FP_EXC_NONRE‐
88 COV for async non-recoverable exception mode, PR_FP_EXC_ASYNC
89 for async recoverable exception mode, PR_FP_EXC_PRECISE for pre‐
90 cise exception mode.
91 PR_GET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
93 Return floating-point exception mode, in the location pointed to
94 by (int *) arg2.
95 PR_SET_KEEPCAPS (since Linux 2.2.18)
97 Set the state of the thread's "keep capabilities" flag, which
98 determines whether the threads's effective and permitted capa‐
99 bility sets are cleared when a change is made to the threads's
100 user IDs such that the threads's real UID, effective UID, and
101 saved set-user-ID all become non-zero when at least one of them
102 previously had the value 0. (By default, these credential sets
103 are cleared). arg2 must be either 0 (capabilities are cleared)
104 or 1 (capabilities are kept). This value will be reset to 0 on
105 subsequent calls to execve(2).
106 PR_GET_KEEPCAPS (since Linux 2.2.18)
108 Return (as the function result) the current state of the calling
109 threads's "keep capabilities" flag.
110 PR_SET_NAME (since Linux 2.6.9)
112 Set the process name for the calling process, using the value in
113 the location pointed to by (char *) arg2. The name can be up to
114 16 bytes long, and should be null terminated if it contains
115 fewer bytes.
116 PR_GET_NAME (since Linux 2.6.11)
118 Return the process name for the calling process, in the buffer
119 pointed to by (char *) arg2. The buffer should allow space for
120 up to 16 bytes; the returned string will be null terminated if
121 it is shorter than that.
122 PR_SET_PDEATHSIG (since Linux 2.1.57)
124 Set the parent process death signal of the calling process to
125 arg2 (either a signal value in the range 1..maxsig, or 0 to
126 clear). This is the signal that the calling process will get
127 when its parent dies. This value is cleared for the child of a
128 fork(2).
129 PR_GET_PDEATHSIG (since Linux 2.3.15)
131 Return the current value of the parent process death signal, in
132 the location pointed to by (int *) arg2.
133 PR_SET_SECCOMP (since Linux 2.6.23)
135 Set the secure computing mode for the calling thread. In the
136 current implementation, arg2 must be 1. After the secure com‐
137 puting mode has been set to 1, the only system calls that the
138 thread is permitted to make are read(2), write(2), _exit(2), and
139 sigreturn(2). Other system calls result in the delivery of a
140 SIGKILL signal. Secure computing mode is useful for number-
141 crunching applications that may need to execute untrusted byte
142 code, perhaps obtained by reading from a pipe or socket. This
143 operation is only available if the kernel is configured with
144 CONFIG_SECCOMP enabled.
145 PR_GET_SECCOMP (since Linux 2.6.23)
147 Return the secure computing mode of the calling thread. Not
148 very useful for the current implementation (mode equals 1), but
149 may be useful for other possible future modes: if the caller is
150 not in secure computing mode, this operation returns 0; if the
151 caller is in secure computing mode, then the prctl() call will
152 cause a SIGKILL signal to be sent to the process. This opera‐
153 tion is only available if the kernel is configured with CON‐
154 FIG_SECCOMP enabled.
155 PR_SET_SECUREBITS (since Linux 2.6.26)
157 Set the "securebits" flags of the calling thread to the value
158 supplied in arg2. See capabilities(7).
159 PR_GET_SECUREBITS (since Linux 2.6.26)
161 Return (as the function result) the "securebits" flags of the
162 calling thread. See capabilities(7).
163 PR_SET_TIMING (since Linux 2.6.0-test4)
165 Set whether to use (normal, traditional) statistical process
166 timing or accurate timestamp based process timing, by passing
167 PR_TIMING_STATISTICAL or PR_TIMING_TIMESTAMP to arg2. PR_TIM‐
168 ING_TIMESTAMP is not currently implemented (attempting to set
169 this mode will yield the error EINVAL).
170 PR_GET_TIMING (since Linux 2.6.0-test4)
172 Return (as the function result) which process timing method is
173 currently in use.
174 PR_SET_TSC (since Linux 2.6.26, x86 only)
176 Set the state of the flag determining whether the timestamp
177 counter can be read by the process. Pass PR_TSC_ENABLE to arg2
178 to allow it to be read, or PR_TSC_SIGSEGV to generate a SIGSEGV
179 when the process tries to read the timestamp counter.
180 PR_GET_TSC (since Linux 2.6.26, x86 only)
182 Return the state of the flag determining whether the timestamp
183 counter can be read, in the location pointed to by (int *) arg2.
184 PR_SET_UNALIGN
186 (Only on: ia64, since Linux 2.3.48; parisc, since Linux 2.6.15;
187 PowerPC, since Linux 2.6.18; Alpha, since Linux 2.6.22) Set
188 unaligned access control bits to arg2. Pass PR_UNALIGN_NOPRINT
189 to silently fix up unaligned user accesses, or PR_UNALIGN_SIGBUS
190 to generate SIGBUS on unaligned user access.
191 PR_GET_UNALIGN
193 (see PR_SET_UNALIGN for information on versions and architec‐
194 tures) Return unaligned access control bits, in the location
195 pointed to by (int *) arg2.
196
198 On success, PR_GET_DUMPABLE, PR_GET_KEEPCAPS, PR_CAPBSET_READ,
199 PR_GET_TIMING, PR_GET_SECUREBITS, and (if it returns) PR_GET_SECCOMP
200 return the non-negative values described above. All other option val‐
201 ues return 0 on success. On error, -1 is returned, and errno is set
202 appropriately.
203
205 EFAULT arg2 is an invalid address.
206 EINVAL The value of option is not recognized.
208 EINVAL arg2 is not valid value for this option.
210 EINVAL option is PR_SET_SECCOMP or PR_SET_SECCOMP, and the kernel was
212 not configured with CONFIG_SECCOMP.
213 EPERM option is PR_SET_SECUREBITS, and the caller does not have the
215 CAP_SETPCAP capability, or tried to unset a "locked" flag, or
216 tried to set a flag whose corresponding locked flag was set (see
217 capabilities(7)).
218 EPERM option is PR_SET_KEEPCAPS, and the callers's
220 SECURE_KEEP_CAPS_LOCKED flag is set (see capabilities(7)).
221 EPERM option is PR_CAPBSET_DROP, and the caller does not have the
223 CAP_SETPCAP capability.
224
226 The prctl() system call was introduced in Linux 2.1.57.
227
229 This call is Linux-specific. IRIX has a prctl() system call (also
230 introduced in Linux 2.1.44 as irix_prctl on the MIPS architecture),
231 with prototype
232 ptrdiff_t prctl(int option, int arg2, int arg3);
234 and options to get the maximum number of processes per user, get the
236 maximum number of processors the calling process can use, find out
237 whether a specified process is currently blocked, get or set the maxi‐
238 mum stack size, etc.
239
241 signal(2), core(5)
242
244 This page is part of release 3.22 of the Linux man-pages project. A
245 description of the project, and information about reporting bugs, can
246 be found at http://www.kernel.org/doc/man-pages/.
247Linux 2008-07-16 PRCTL(2)