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Man Pages


Manual Reference Pages  -  SHMCAT (1)

NAME

shmcat - dump shared memory segments, files, standard input and/or text

CONTENTS

Synopsis
Description
Options
Operands
Exit Codes
Notes
Author

SYNOPSIS

shmcat [ OPTION ]... [ OPERAND ]...

DESCRIPTION

Dump shared memory segments, files, standard input and/or text to standard output. If no OPERAND is given, read standard input only. If more than one OPERAND is given, dump them in order. If some of the OPERANDs cannot be read, shmcat prints an error message to standard error and tries to continue with the other OPERANDs.

Most modern systems support two APIs for shared memory:

The older one is commonly known as the System V API. It uses numeric keys and IDs as identifiers and consists of system calls like shmget(2), shmat(2) and shmdt(2).

The newer API is called the POSIX shared memory API. It uses names in string form as identifiers. It treats shared memory similar to files, which are opened with shm_open(3) and then mapped into the program address space via mmap(2). Please note that POSIX shared memory is not supported by all versions of shmcat.

If shmcat has been compiled without getopt_long(3) support, only the short, one character OPTIONs and OPERANDs can be used. Otherwise the long ones are also available. When a long OPTION or OPERAND needs an argument, the short versions do so, as well.

OPTIONS

-h, -?, --help
  Display usage information and quit without dumping anything.
-V, --version
  Show version information and quit without further action.

OPERANDS

-f, --file=FILENAME
  Dump the contents of the given file.
-i, --stdin
  Dump standard input.
-M, --shmkey=KEY
  Dump the System V shared memory segment with the given key. The key can be given as a decimal (no prefix), octal (prefix 0), or hexadecimal (prefix 0x) number. It can, for example, be obtained using the ipcs(1) or the ftok(1) tool.
-m, --shmid=ID
  Dump the System V shared memory segment with the given id. The id can be given as a decimal (no prefix), octal (prefix 0), or hexadecimal (prefix 0x) number. It can, for example, be obtained using the ipcs(1) tool.
-n, --newline
  Add a line feed.
-p, --posix-shm=NAME
  Dump the POSIX shared memory segment with the given name (not supported in all installations).
-t, --text=TEXT
  Print the given text.

EXIT CODES

0 No errors, every OPERAND requested was dumped
1 There was an error while dumping at least one OPERAND, but the program continued with the other OPERANDs (if given)
2 There was a fatal error, usually this means that shmcat could not write to standard output
10 Wrong usage of the program

NOTES

Usually, when you dump shared memory segments, you should redirect the output of shmcat to a file or a program like od(1), because shared memory data usually has a binary form and thus it may contain non-printable characters. You also probably want to suspend the processes writing to the shared memory object in order to get a consistent dump.

AUTHOR

Stefan Gast

SEE ALSO

ftok(1), ipcs(1), shmat(2), shmget(2), shm_open(3)
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shmcat(1) SHMCAT (1) November 2012

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