| 1 | .\" Copyright (c) 1980 Regents of the University of California.
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| 2 | .\" All rights reserved. The Berkeley software License Agreement
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| 3 | .\" specifies the terms and conditions for redistribution.
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| 4 | .\"
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| 5 | .\" @(#)open.2 6.4 (Berkeley) 5/14/86
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| 6 | .\"
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| 7 | .TH OPEN 2 "May 14, 1986"
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| 8 | .UC 4
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| 9 | .SH NAME
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| 10 | open \- open a file for reading or writing, or create a new file
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| 11 | .SH SYNOPSIS
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| 12 | .nf
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| 13 | .ft B
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| 14 | #include <sys/types.h>
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| 15 | #include <fcntl.h>
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| 16 |
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| 17 | int open(const char *\fIpath\fP, int \fIflags\fP \fR[\fP, mode_t \fImode\fP\fR]\fP)
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| 18 | .ft R
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| 19 | .fi
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| 20 | .SH DESCRIPTION
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| 21 | .B Open
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| 22 | opens the file
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| 23 | .I path
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| 24 | for reading and/or writing, as specified by the
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| 25 | .I flags
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| 26 | argument and returns a descriptor for that file.
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| 27 | The
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| 28 | .I flags
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| 29 | argument may indicate the file is to be
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| 30 | created if it does not already exist (by specifying the
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| 31 | O_CREAT flag), in which case the file is created with mode
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| 32 | .I mode
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| 33 | as described in
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| 34 | .BR chmod (2)
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| 35 | and modified by the process' umask value (see
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| 36 | .BR umask (2)).
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| 37 | .PP
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| 38 | .I Path
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| 39 | is the address of a string of ASCII characters representing
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| 40 | a path name, terminated by a null character.
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| 41 | The flags specified are formed by
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| 42 | .IR or 'ing
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| 43 | the following values
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| 44 | .PP
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| 45 | .RS
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| 46 | .ta +12n
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| 47 | .nf
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| 48 | O_RDONLY open for reading only
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| 49 | O_WRONLY open for writing only
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| 50 | O_RDWR open for reading and writing
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| 51 | O_NONBLOCK do not block on open
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| 52 | O_APPEND append on each write
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| 53 | O_CREAT create file if it does not exist
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| 54 | O_TRUNC truncate size to 0
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| 55 | O_EXCL error if create and file exists
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| 56 | .fi
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| 57 | .DT
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| 58 | .RE
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| 59 | .PP
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| 60 | Opening a file with O_APPEND set causes each write on the file
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| 61 | to be appended to the end. If O_TRUNC is specified and the
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| 62 | file exists, the file is truncated to zero length.
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| 63 | If O_EXCL is set with O_CREAT, then if the file already
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| 64 | exists, the open returns an error. This can be used to
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| 65 | implement a simple exclusive access locking mechanism.
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| 66 | If O_EXCL is set and the last component of the pathname is
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| 67 | a symbolic link, the open will fail even if the symbolic
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| 68 | link points to a non-existent name.
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| 69 | If the O_NONBLOCK flag is specified and the open call would result
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| 70 | in the process being blocked for some reason, the open returns immediately.
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| 71 | .PP
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| 72 | Upon successful completion a non-negative integer termed a
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| 73 | file descriptor is returned.
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| 74 | The file pointer used to mark the current position within the
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| 75 | file is set to the beginning of the file.
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| 76 | .PP
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| 77 | The new descriptor is set to remain open across
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| 78 | .BR execve
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| 79 | system calls; see
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| 80 | .BR close (2).
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| 81 | .PP
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| 82 | The system imposes a limit on the number of descriptors
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| 83 | open simultaneously by one process.
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| 84 | .SH "ERRORS
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| 85 | The named file is opened unless one or more of the
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| 86 | following are true:
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| 87 | .TP 15
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| 88 | [ENOTDIR]
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| 89 | A component of the path prefix is not a directory.
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| 90 | .TP 15
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| 91 | [ENAMETOOLONG]
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| 92 | The path name exceeds PATH_MAX characters.
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| 93 | .TP 15
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| 94 | [ENOENT]
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| 95 | O_CREAT is not set and the named file does not exist.
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| 96 | .TP 15
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| 97 | [ENOENT]
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| 98 | A component of the path name that must exist does not exist.
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| 99 | .TP 15
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| 100 | [EACCES]
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| 101 | Search permission is denied for a component of the path prefix.
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| 102 | .TP 15
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| 103 | [EACCES]
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| 104 | The required permissions (for reading and/or writing)
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| 105 | are denied for the named file.
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| 106 | .TP 15
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| 107 | [EACCES]
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| 108 | O_CREAT is specified,
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| 109 | the file does not exist,
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| 110 | and the directory in which it is to be created
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| 111 | does not permit writing.
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| 112 | .TP 15
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| 113 | [EACCES]
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| 114 | A device to be opened for writing is physically write protected.
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| 115 | .TP 15
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| 116 | [ELOOP]
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| 117 | Too many symbolic links were encountered in translating the pathname.
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| 118 | (Minix-vmd)
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| 119 | .TP 15
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| 120 | [EISDIR]
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| 121 | The named file is a directory, and the arguments specify
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| 122 | it is to be opened for writing.
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| 123 | .TP 15
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| 124 | [EROFS]
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| 125 | The named file resides on a read-only file system,
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| 126 | and the file is to be modified.
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| 127 | .TP 15
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| 128 | [EMFILE]
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| 129 | The system limit for open file descriptors per process has already been reached.
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| 130 | .TP 15
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| 131 | [ENFILE]
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| 132 | The system file table is full.
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| 133 | .TP 15
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| 134 | [ENXIO]
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| 135 | The named file is a character special or block
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| 136 | special file, and the device associated with this special file
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| 137 | does not exist.
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| 138 | .TP 15
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| 139 | [ENOSPC]
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| 140 | O_CREAT is specified,
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| 141 | the file does not exist,
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| 142 | and the directory in which the entry for the new file is being placed
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| 143 | cannot be extended because there is no space left on the file
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| 144 | system containing the directory.
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| 145 | .TP 15
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| 146 | [ENOSPC]
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| 147 | O_CREAT is specified,
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| 148 | the file does not exist,
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| 149 | and there are no free inodes on the file system on which the
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| 150 | file is being created.
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| 151 | .ig
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| 152 | .TP 15
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| 153 | [EDQUOT]
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| 154 | O_CREAT is specified,
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| 155 | the file does not exist,
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| 156 | and the directory in which the entry for the new fie
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| 157 | is being placed cannot be extended because the
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| 158 | user's quota of disk blocks on the file system
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| 159 | containing the directory has been exhausted.
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| 160 | .TP 15
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| 161 | [EDQUOT]
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| 162 | O_CREAT is specified,
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| 163 | the file does not exist,
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| 164 | and the user's quota of inodes on the file system on
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| 165 | which the file is being created has been exhausted.
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| 166 | ..
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| 167 | .TP 15
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| 168 | [EIO]
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| 169 | An I/O error occurred while making the directory entry or
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| 170 | allocating the inode for O_CREAT.
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| 171 | .TP 15
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| 172 | [EFAULT]
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| 173 | .I Path
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| 174 | points outside the process's allocated address space.
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| 175 | .TP 15
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| 176 | [EEXIST]
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| 177 | O_CREAT and O_EXCL were specified and the file exists.
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| 178 | .SH "SEE ALSO"
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| 179 | .BR chmod (2),
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| 180 | .BR close (2),
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| 181 | .BR dup (2),
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| 182 | .BR fcntl (2),
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| 183 | .BR lseek (2),
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| 184 | .BR read (2),
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| 185 | .BR write (2),
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| 186 | .BR umask (2).
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