man3/getmntent.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified Sat Jul 24 21:46:57 1993 by Rik Faith (faith@cs.unc.edu)
  30 .\" Modified 961109, 031115, aeb
  31 .\"
  32 .TH GETMNTENT 3  2019-03-06 "" "Linux Programmer's Manual"
  33 .SH NAME
  34 getmntent, setmntent, addmntent, endmntent, hasmntopt,
  35 getmntent_r \- get filesystem descriptor file entry
  36 .SH SYNOPSIS
  37 .nf
  38 .B #include <stdio.h>
  39 .B #include <mntent.h>
  40 .PP
  41 .BI "FILE *setmntent(const char *" filename ", const char *" type );
  42 .PP
  43 .BI "struct mntent *getmntent(FILE *" stream );
  44 .PP
  45 .BI "int addmntent(FILE *" stream ", const struct mntent *" mnt );
  46 .PP
  47 .BI "int endmntent(FILE *" streamp );
  48 .PP
  49 .BI "char *hasmntopt(const struct mntent *" mnt ", const char *" opt );
  50
  51 /* GNU extension */
  52 .B #include <mntent.h>
  53 .PP
  54 .BI "struct mntent *getmntent_r(FILE *" streamp ", struct mntent *" mntbuf ,
  55 .BI "                           char *" buf ", int " buflen );
  56 .fi
  57 .PP
  58 .in -4n
  59 Feature Test Macro Requirements for glibc (see
  60 .BR feature_test_macros (7)):
  61 .in
  62 .PP
  63 .BR getmntent_r ():
  64     Since glibc 2.19:
  65         _DEFAULT_SOURCE
  66     Glibc 2.19 and earlier:
  67         _BSD_SOURCE || _SVID_SOURCE
  68 .SH DESCRIPTION
  69 These routines are used to access the filesystem description file
  70 .I /etc/fstab
  71 and the mounted filesystem description file
  72 .IR /etc/mtab .
  73 .PP
  74 The
  75 .BR setmntent ()
  76 function opens the filesystem description file
  77 .I filename
  78 and returns a file pointer which can be used by
  79 .BR getmntent ().
  80 The argument
  81 .I type
  82 is the type of access
  83 required and can take the same values as the
  84 .I mode
  85 argument of
  86 .BR fopen (3).
  87 The returned stream should be closed using
  88 .BR endmntent ()
  89 rather than
  90 .BR fclose (3).
  91 .PP
  92 The
  93 .BR getmntent ()
  94 function reads the next line of the filesystem
  95 description file from
  96 .I stream
  97 and returns a pointer to a structure
  98 containing the broken out fields from a line in the file.
  99 The pointer
 100 points to a static area of memory which is overwritten by subsequent
 101 calls to
 102 .BR getmntent ().
 103 .PP
 104 The
 105 .BR addmntent ()
 106 function adds the
 107 .I mntent
 108 structure
 109 .I mnt
 110 to
 111 the end of the open
 112 .IR stream .
 113 .PP
 114 The
 115 .BR endmntent ()
 116 function closes the
 117 .IR stream
 118 associated with the filesystem description file.
 119 .PP
 120 The
 121 .BR hasmntopt ()
 122 function scans the
 123 .I mnt_opts
 124 field (see below)
 125 of the
 126 .I mntent
 127 structure
 128 .I mnt
 129 for a substring that matches
 130 .IR opt .
 131 See
 132 .I <mntent.h>
 133 and
 134 .BR mount (8)
 135 for valid mount options.
 136 .PP
 137 The reentrant
 138 .BR getmntent_r ()
 139 function is similar to
 140 .BR getmntent (),
 141 but stores the
 142 .IR "struct mount"
 143 in the provided
 144 .I *mntbuf
 145 and stores the strings pointed to by the entries in that struct
 146 in the provided array
 147 .I buf
 148 of size
 149 .IR buflen .
 150 .PP
 151 The
 152 .I mntent
 153 structure is defined in
 154 .I <mntent.h>
 155 as follows:
 156 .PP
 157 .in +4n
 158 .EX
 159 struct mntent {
 160     char *mnt_fsname;   /* name of mounted filesystem */
 161     char *mnt_dir;      /* filesystem path prefix */
 162     char *mnt_type;     /* mount type (see mntent.h) */
 163     char *mnt_opts;     /* mount options (see mntent.h) */
 164     int   mnt_freq;     /* dump frequency in days */
 165     int   mnt_passno;   /* pass number on parallel fsck */
 166 };
 167 .EE
 168 .in
 169 .PP
 170 Since fields in the mtab and fstab files are separated by whitespace,
 171 octal escapes are used to represent the characters space (\e040),
 172 tab (\e011), newline (\e012), and backslash (\e\e) in those files
 173 when they occur in one of the four strings in a
 174 .I mntent
 175 structure.
 176 The routines
 177 .BR addmntent ()
 178 and
 179 .BR getmntent ()
 180 will convert
 181 from string representation to escaped representation and back.
 182 When converting from escaped representation, the sequence \e134 is
 183 also converted to a backslash.
 184 .SH RETURN VALUE
 185 The
 186 .BR getmntent ()
 187 and
 188 .BR getmntent_r ()
 189 functions return
 190 a pointer to the
 191 .I mntent
 192 structure or NULL on failure.
 193 .PP
 194 The
 195 .BR addmntent ()
 196 function returns 0 on success and 1 on failure.
 197 .PP
 198 The
 199 .BR endmntent ()
 200 function always returns 1.
 201 .PP
 202 The
 203 .BR hasmntopt ()
 204 function returns the address of the substring if
 205 a match is found and NULL otherwise.
 206 .SH FILES
 207 .TP
 208 .I /etc/fstab
 209 filesystem description file
 210 .TP
 211 .I /etc/mtab
 212 mounted filesystem description file
 213 .SH ATTRIBUTES
 214 For an explanation of the terms used in this section, see
 215 .BR attributes (7).
 216 .ad l
 217 .TS
 218 allbox;
 219 lbw13 lb lbw31
 220 l l l.
 221 Interface       Attribute       Value
 222 T{
 223 .BR setmntent (),
 224 .BR endmntent (),
 225 .BR hasmntopt ()
 226 T}      Thread safety   MT-Safe
 227 T{
 228 .BR getmntent ()
 229 T}      Thread safety   MT-Unsafe race:mntentbuf locale
 230 T{
 231 .BR addmntent ()
 232 T}      Thread safety   MT-Safe race:stream locale
 233 T{
 234 .BR getmntent_r ()
 235 T}      Thread safety   MT-Safe locale
 236 .TE
 237 .ad
 238 .SH CONFORMING TO
 239 The nonreentrant functions are from SunOS 4.1.3.
 240 A routine
 241 .BR getmntent_r ()
 242 was introduced in HP-UX 10, but it returns an int.
 243 The prototype shown above is glibc-only.
 244 .SH NOTES
 245 System V also has a
 246 .BR getmntent ()
 247 function but the calling sequence
 248 differs, and the returned structure is different.
 249 Under System V
 250 .I /etc/mnttab
 251 is used.
 252 4.4BSD and Digital UNIX have a routine
 253 .BR getmntinfo (),
 254 a wrapper around the system call
 255 .BR getfsstat ().
 256 .SH SEE ALSO
 257 .BR fopen (3),
 258 .BR fstab (5),
 259 .BR mount (8)