99 lines
2.3 KiB
Plaintext
99 lines
2.3 KiB
Plaintext
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.TH SNAP 6
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.SH NAME
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snap \- process snapshots
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.SH DESCRIPTION
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Process snapshots are used to
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save a process image for debugging on
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another machine or at another time.
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They are like old Unix core dumps but
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can hold multiple process images and
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are smaller.
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.PP
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The first line of a snapshot begins with the prefix
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``process snapshot'' and often contains
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other information as well, such as creation time,
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user name, system name, cpu type, and kernel type.
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This information is intended for humans, not programs.
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Programs reading snapshots should only
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check that this line begins with the specified prefix.
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.PP
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Throughout the rest of the snapshot, decimal strings are
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always right-justified, blank-padded to at least 11 characters,
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and followed by a single space character.
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.PP
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The rest of the snapshot is one or more records,
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each of which begins with a one-line header.
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This header is a decimal process id followed by
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an identification string, which denotes the type of
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data in the record.
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.PP
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Records of type
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.BR fd ,
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.BR fpregs ,
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.BR kregs ,
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.BR noteid ,
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.BR ns ,
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.BR proc ,
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.BR regs ,
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.BR segment ,
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and
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.BR status
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are all formatted as a decimal number
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.I n
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followed by
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.I n
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bytes of data.
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This data is the contents of the file
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of the same name found in
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.BR /proc .
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.PP
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The format of the
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.B mem
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and
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.B text
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sections is not as simple.
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These sections contain one or more page descriptions.
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Each describes a one kilobyte page of data.
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If the section is not a multiple of a kilobyte in size,
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the last page will be shorter.
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Each description begins with a one-byte
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flag.
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If the flag is
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.BR r ,
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then it is followed by
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a page of binary data.
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If the flag is
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.BR z ,
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then the data is understood to be zeros,
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and is omitted.
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If the flag is
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.B m
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or
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.BR t ,
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then it is followed by two decimal strings
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.I p
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and
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.IR o ,
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indicating that this page is the same
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as the page at offset
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.I o
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of the memory or text
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segment for process
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.IR p .
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This data must have been previously
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described in the snapshot, and the offset
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must be a multiple of a kilobyte.
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.PP
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It is not guaranteed that any of the sections
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described above be in a process snapshot,
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although the snapshot quickly becomes useless when
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too much is missing.
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.PP
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Memory and text images may be incomplete.
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The memory or text file for a given process
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may be split across multiple disjoint sections
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in the snapshot.
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.SH SEE ALSO
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.IR proc (3),
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.IR snap (4).
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