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38 .Nd checkpoint or restore a process
45 .Fn sys_checkpoint "int type" "int fd" "pid_t pid" "int retval"
49 system call executes a checkpoint function as specified by
51 Supported types are as follows:
52 .Bl -tag -width ".Dv CKPT_FREEZE" -offset indent
54 Generate a checkpoint file.
57 must be -1 or the pid of the current process.
58 The checkpoint file will be written out to
62 is unused but must be specified as -1.
67 are both specified as -1, the system will generate a checkpoint file
68 using the system checkpoint template.
70 This function returns 0 on success, -1 on error, and typically 1
72 The value returned on resume is controlled by the
76 when resuming a checkpoint file.
77 A user program which installs its own
79 signal handler and calls
81 manually thus has control over both termination/continuance and
84 Restore a checkpointed program.
87 must be specified as -1, and
89 represents the checkpoint file.
92 specifies the value returned to the resumed program if
96 The checkpointed program will replace the current program, similar to
102 Upon successful completion, the value 0 is typically returned.
103 A checkpoint being resumed typically returns a positive value;
104 otherwise the value -1 is returned and the global variable
106 is set to indicate the error.
108 .Bd -literal -offset indent -compact
110 * Demonstrate checkpointing. Use control-E to checkpoint
111 * the program and 'checkpt -r x.ckpt' to resume it.
113 #include <sys/types.h>
114 #include <sys/signal.h>
115 #include <sys/checkpoint.h>
121 void docheckpoint(void);
132 main(int argc, char** argv)
136 signal(SIGCKPT, dockpt);
139 printf("iteration: %d\en", i);
144 printf("Checkpoint requested\en");
157 fd = open("x.ckpt", O_RDWR|O_CREAT|O_TRUNC, 0666);
159 printf("unable to create checkpoint file: %s\en",
164 ret = sys_checkpoint(CKPT_FREEZE, fd, -1, -1);
166 printf("unable to checkpoint: %s\en",
168 } else if (ret == 0) {
169 printf("checkpoint successful, continuing\en");
170 } else if (ret == 1) {
171 printf("resuming from checkpoint.\en");
173 printf("unknown return value %d from sys_checkpoint\en", ret);
176 /* note that the file descriptor is still valid on a resume */
185 is not a valid regular file, socket descriptor, or pipe.
187 all systems necessarily support checkpointing to sockets and pipes.
189 The caller does not have permission to issue the checkpoint command.
190 Checkpointing may be restricted or disabled using sysctls.
192 An I/O error occurred while reading from the file system.
194 An invalid parameter was specified.
196 .Sh CHECKPOINT FEATURES
197 The system checkpointing code will save the process register state (including
198 floating point registers), signal state, file descriptors representing
199 regular files or directories (anything that can be converted into a file
200 handle for storage), and both shared and private memory mappings.
201 Private, writable mappings are copied to the checkpoint file while shared
202 mappings and stored by referencing the file handle and offset.
203 Note that the system checkpointing code does not retain references to
204 deleted files, so mappings and open descriptors of deleted files
206 Unpredictable operation will occur if a checkpoint-unaware program
207 is restored and some of the underlying files mapped by the program
210 The system checkpointing code is not able to retain the process pid, process
211 group, user/group creds, or descriptors 0, 1, and 2.
212 These will be inherited from whomever restores the checkpoint.
214 When a checkpointed program is restored modified private mappings will
215 be mapped from the checkpoint file itself, but major portions of the
216 original program binary will be mapped from the original program binary.
217 If the resumed program is checkpointed again the system will automatically
218 copy any mappings from the original checkpoint file to the new one, since
219 the original is likely being replaced.
220 The caller must not truncate the existing checkpoint file when creating
221 a new one or specify the existing file's file descriptor as the new
222 one as this will destroy the data that the checkpoint operation needs
223 to copy to the new file.
224 It is best to checkpoint to a new file and then rename-over the old, or to
226 the old file before creating the new
227 one so it remains valid as long as the program continues to run.
229 Threaded programs cannot currently be checkpointed.
231 reduced to a single thread before it can be safely checkpointed.
234 mappings cannot currently be checkpointed.
235 A program must restore such mappings manually on resumption.
236 Only regular file and
237 anonymous memory mappings are checkpointed and restored.
238 Device and other special mappings are not.
239 Only regular file descriptors are checkpointed and restored.
240 Devices, pipes, sockets, and other special descriptors are not.
241 Memory wiring states are not checkpointed or restored.
243 states are not checkpointed or restored.
244 Basic mapping permissions are checkpointed and restored.
248 controls which group can use system checkpointing.
249 By default, only users in the
251 group are allowed to checkpoint and restore processes.
252 To allow users in any group to have this capability (risky), set sysctl
256 Two signals are associated with checkpointing.
258 is delivered via the tty ckpt character, usually control-E.
259 Its default action is to checkpoint a program and continue running it.
262 signal can only be delivered by
264 Its default action is to checkpoint a program and then exit.
266 might not be implemented by the system.
267 Both signals are defined to
268 be greater or equal to signal 32 and cannot be manipulated using legacy
271 If a program overrides the default action for a checkpoint signal the
272 system will not undertake any action of its own.
273 The program may issue
274 the checkpoint command from the signal handler itself or simply set a
275 reminder for later action.
276 It is usually safest to set a reminder and
277 do the actual checkpointing from your main loop.
284 function call appeared in