man3/getmntent.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" References consulted:
   6 .\"     Linux libc source code
   7 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
   8 .\"     386BSD man pages
   9 .\" Modified Sat Jul 24 21:46:57 1993 by Rik Faith (faith@cs.unc.edu)
  10 .\" Modified 961109, 031115, aeb
  11 .\"
  12 .TH GETMNTENT 3  2021-03-22 "" "Linux Programmer's Manual"
  13 .SH NAME
  14 getmntent, setmntent, addmntent, endmntent, hasmntopt,
  15 getmntent_r \- get filesystem descriptor file entry
  16 .SH LIBRARY
  17 Standard C library
  18 .RI ( libc ", " \-lc )
  19 .SH SYNOPSIS
  20 .nf
  21 .B #include <stdio.h>
  22 .B #include <mntent.h>
  23 .PP
  24 .BI "FILE *setmntent(const char *" filename ", const char *" type );
  25 .PP
  26 .BI "struct mntent *getmntent(FILE *" stream );
  27 .PP
  28 .BI "int addmntent(FILE *restrict " stream ,
  29 .BI "              const struct mntent *restrict " mnt );
  30 .PP
  31 .BI "int endmntent(FILE *" streamp );
  32 .PP
  33 .BI "char *hasmntopt(const struct mntent *" mnt ", const char *" opt );
  34 .PP
  35 /* GNU extension */
  36 .B #include <mntent.h>
  37 .PP
  38 .BI "struct mntent *getmntent_r(FILE *restrict " streamp ,
  39 .BI "              struct mntent *restrict " mntbuf ,
  40 .BI "              char *restrict " buf ", int " buflen );
  41 .fi
  42 .PP
  43 .RS -4
  44 Feature Test Macro Requirements for glibc (see
  45 .BR feature_test_macros (7)):
  46 .RE
  47 .PP
  48 .BR getmntent_r ():
  49 .nf
  50     Since glibc 2.19:
  51         _DEFAULT_SOURCE
  52     Glibc 2.19 and earlier:
  53         _BSD_SOURCE || _SVID_SOURCE
  54 .fi
  55 .SH DESCRIPTION
  56 These routines are used to access the filesystem description file
  57 .I /etc/fstab
  58 and the mounted filesystem description file
  59 .IR /etc/mtab .
  60 .PP
  61 The
  62 .BR setmntent ()
  63 function opens the filesystem description file
  64 .I filename
  65 and returns a file pointer which can be used by
  66 .BR getmntent ().
  67 The argument
  68 .I type
  69 is the type of access
  70 required and can take the same values as the
  71 .I mode
  72 argument of
  73 .BR fopen (3).
  74 The returned stream should be closed using
  75 .BR endmntent ()
  76 rather than
  77 .BR fclose (3).
  78 .PP
  79 The
  80 .BR getmntent ()
  81 function reads the next line of the filesystem
  82 description file from
  83 .I stream
  84 and returns a pointer to a structure
  85 containing the broken out fields from a line in the file.
  86 The pointer
  87 points to a static area of memory which is overwritten by subsequent
  88 calls to
  89 .BR getmntent ().
  90 .PP
  91 The
  92 .BR addmntent ()
  93 function adds the
  94 .I mntent
  95 structure
  96 .I mnt
  97 to
  98 the end of the open
  99 .IR stream .
 100 .PP
 101 The
 102 .BR endmntent ()
 103 function closes the
 104 .IR stream
 105 associated with the filesystem description file.
 106 .PP
 107 The
 108 .BR hasmntopt ()
 109 function scans the
 110 .I mnt_opts
 111 field (see below)
 112 of the
 113 .I mntent
 114 structure
 115 .I mnt
 116 for a substring that matches
 117 .IR opt .
 118 See
 119 .I <mntent.h>
 120 and
 121 .BR mount (8)
 122 for valid mount options.
 123 .PP
 124 The reentrant
 125 .BR getmntent_r ()
 126 function is similar to
 127 .BR getmntent (),
 128 but stores the
 129 .IR "struct mount"
 130 in the provided
 131 .I *mntbuf
 132 and stores the strings pointed to by the entries in that struct
 133 in the provided array
 134 .I buf
 135 of size
 136 .IR buflen .
 137 .PP
 138 The
 139 .I mntent
 140 structure is defined in
 141 .I <mntent.h>
 142 as follows:
 143 .PP
 144 .in +4n
 145 .EX
 146 struct mntent {
 147     char *mnt_fsname;   /* name of mounted filesystem */
 148     char *mnt_dir;      /* filesystem path prefix */
 149     char *mnt_type;     /* mount type (see mntent.h) */
 150     char *mnt_opts;     /* mount options (see mntent.h) */
 151     int   mnt_freq;     /* dump frequency in days */
 152     int   mnt_passno;   /* pass number on parallel fsck */
 153 };
 154 .EE
 155 .in
 156 .PP
 157 Since fields in the mtab and fstab files are separated by whitespace,
 158 octal escapes are used to represent the characters space (\e040),
 159 tab (\e011), newline (\e012), and backslash (\e\e) in those files
 160 when they occur in one of the four strings in a
 161 .I mntent
 162 structure.
 163 The routines
 164 .BR addmntent ()
 165 and
 166 .BR getmntent ()
 167 will convert
 168 from string representation to escaped representation and back.
 169 When converting from escaped representation, the sequence \e134 is
 170 also converted to a backslash.
 171 .SH RETURN VALUE
 172 The
 173 .BR getmntent ()
 174 and
 175 .BR getmntent_r ()
 176 functions return
 177 a pointer to the
 178 .I mntent
 179 structure or NULL on failure.
 180 .PP
 181 The
 182 .BR addmntent ()
 183 function returns 0 on success and 1 on failure.
 184 .PP
 185 The
 186 .BR endmntent ()
 187 function always returns 1.
 188 .PP
 189 The
 190 .BR hasmntopt ()
 191 function returns the address of the substring if
 192 a match is found and NULL otherwise.
 193 .SH FILES
 194 .TP
 195 .I /etc/fstab
 196 filesystem description file
 197 .TP
 198 .I /etc/mtab
 199 mounted filesystem description file
 200 .SH ATTRIBUTES
 201 For an explanation of the terms used in this section, see
 202 .BR attributes (7).
 203 .ad l
 204 .nh
 205 .TS
 206 allbox;
 207 lb lb lbx
 208 l l l.
 209 Interface       Attribute       Value
 210 T{
 211 .BR setmntent (),
 212 .BR endmntent (),
 213 .BR hasmntopt ()
 214 T}      Thread safety   MT-Safe
 215 T{
 216 .BR getmntent ()
 217 T}      Thread safety   T{
 218 MT-Unsafe race:mntentbuf locale
 219 T}
 220 T{
 221 .BR addmntent ()
 222 T}      Thread safety   T{
 223 MT-Safe race:stream locale
 224 T}
 225 T{
 226 .BR getmntent_r ()
 227 T}      Thread safety   MT-Safe locale
 228 .TE
 229 .hy
 230 .ad
 231 .sp 1
 232 .SH CONFORMING TO
 233 The nonreentrant functions are from SunOS 4.1.3.
 234 A routine
 235 .BR getmntent_r ()
 236 was introduced in HP-UX 10, but it returns an
 237 .IR int .
 238 The prototype shown above is glibc-only.
 239 .SH NOTES
 240 System V also has a
 241 .BR getmntent ()
 242 function but the calling sequence
 243 differs, and the returned structure is different.
 244 Under System V
 245 .I /etc/mnttab
 246 is used.
 247 4.4BSD and Digital UNIX have a routine
 248 .BR getmntinfo (),
 249 a wrapper around the system call
 250 .BR getfsstat ().
 251 .SH SEE ALSO
 252 .BR fopen (3),
 253 .BR fstab (5),
 254 .BR mount (8)