User`s guide

D2.1.4 IST-033576

or session leader. When in doubt, try using the ’-j’ option to ’ps’ to show PGID

and SID columns. The –tree ﬂag to cr_checkpoint requests a checkpoint of the

process with the given pid, and all its descendants (excluding those who’s parent

has exited and thus become children of the init process). This is the same as the

grouping shown by the output of the pstree command. NEW: The behavior in

0.6.0 is a change from previous BLCR releases in which the –pid option (below)

was the default.

When checkpointing multiple processes using one of the scope arguments

other then –pid, all the pipes among the processes are saved and restored. Pipes

to/from processes not within the checkpoint scope are not saved (these will be

replaced at restart time by the stdin or stdout of the cr_restart process). While

cr_checkpoint will accept a process group or session identiﬁer as a scope argu-

ment, BLCR does not currently restore the pgid or sid of restarted processes. In-

stead restored processes inherit the pgid and sid of the cr_restart process. This

is considered a sane default because an unmodiﬁed parent (such as a shell) of

cr_restart would lose job control over the processes if these identiﬁers are re-

stored. A future BLCR release will include the ability to request restore of these

identiﬁers.

Files that contain checkpoints are called context ﬁles. By default, they are

named context.ID, where ID is the pid, pgid or sid that was checkpointed, and are

stored in the current working directory of the cr_checkpoint process. You may

specify an alternate name and location of the context ﬁle via the -f option.

There are a number of other options that cr_checkpoint provides. See the man

page (or cr_checkpoint –help) for details.

B.4.4 Restarting the process

To successfully restart from a context ﬁle, certain conditions must be met:

• The PIDs of processes in the context ﬁle must NOT be in use.

• The original executable must still exist, and its contents must be unchanged,

except if –save-private and –save-shared option have been set at check-

point.

• All shared libraries used by the executable must exist, and their contents

must be unchanged, except if –save-all option has been used for the check-

point.

• Because BLCR saves and restore most open ﬁles "by reference" (storing

pathnames rather than ﬁle contents), the following should be true of ﬁles

that were open when the checkpoint was taken, though certain applications

may be more tolerant than these rules imply:

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