1 MNTTAB(4) File Formats MNTTAB(4)
2
3
4
5 NAME
6 mnttab - mounted file system table
7
8 DESCRIPTION
9 The file /etc/mnttab is really a file system that provides read-only
10 access to the table of mounted file systems for the current host.
11 /etc/mnttab is read by programs using the routines described in
12 getmntent(3C). Mounting a file system adds an entry to this table.
13 Unmounting removes an entry from this table. Remounting a file system
14 causes the information in the mounted file system table to be updated
15 to reflect any changes caused by the remount. The list is maintained by
16 the kernel in order of mount time. That is, the first mounted file
17 system is first in the list and the most recently mounted file system
18 is last. When mounted on a mount point the file system appears as a
19 regular file containing the current mnttab information.
20
21
22 Each entry is a line of fields separated by TABs in the form:
23
24 special mount_point fstype options time
25
26
27
28 where:
29
30 special
31 The name of the resource that has been mounted.
32
33
34 mount_point
35 The pathname of the directory on which the filesystem is
36 mounted.
37
38
39 fstype
40 The file system type of the mounted file system.
41
42
43 options
44 The mount options. See respective mount file system man
45 page in the See Also section below.
46
47
48 time
49 The time at which the file system was mounted.
50
51
52
53 Examples of entries for the special field include the pathname of a
54 block-special device, the name of a remote file system in the form of
55 host:pathname, or the name of a swap file, for example, a file made
56 with mkfile(1M).
57
58 IOCTLS
59 The following ioctl(2) calls are supported:
60
61 MNTIOC_NMNTS
62 Returns the count of mounted resources in the
63 current snapshot in the uint32_t pointed to by
64 arg.
65
66
67 MNTIOC_GETDEVLIST
68 Returns an array of uint32_t's that is twice as
69 long as the length returned by MNTIOC_NMNTS. Each
70 pair of numbers is the major and minor device
71 number for the file system at the corresponding
72 line in the current /etc/mnttab snapshot. arg
73 points to the memory buffer to receive the device
74 number information.
75
76
77 MNTIOC_SETTAG
78 Sets a tag word into the options list for a
79 mounted file system. A tag is a notation that will
80 appear in the options string of a mounted file
81 system but it is not recognized or interpreted by
82 the file system code. arg points to a filled in
83 mnttagdesc structure, as shown in the following
84 example:
85
86 uint_t mtd_major; /* major number for mounted fs */
87 uint_t mtd_minor; /* minor number for mounted fs */
88 char *mtd_mntpt; /* mount point of file system */
89 char *mtd_tag; /* tag to set/clear */
90
91 If the tag already exists then it is marked as set
92 but not re-added. Tags can be at most
93 MAX_MNTOPT_TAG long.
94
95 Use of this ioctl is restricted to processes with
96 the {PRIV_SYS_MOUNT} privilege.
97
98
99 MNTIOC_CLRTAG
100 Marks a tag in the options list for a mounted file
101 system as not set. arg points to the same
102 structure as MNTIOC_SETTAG, which identifies the
103 file system and tag to be cleared.
104
105 Use of this ioctl is restricted to processes with
106 the {PRIV_SYS_MOUNT} privilege.
107
108
109 ERRORS
110 EFAULT
111 The arg pointer in an MNTIOC_ ioctl call pointed to an
112 inaccessible memory location or a character pointer in
113 a mnttagdesc structure pointed to an inaccessible
114 memory location.
115
116
117 EINVAL
118 The tag specified in a MNTIOC_SETTAG call already
119 exists as a file system option, or the tag specified in
120 a MNTIOC_CLRTAG call does not exist.
121
122
123 ENAMETOOLONG
124 The tag specified in a MNTIOC_SETTAG call is too long
125 or the tag would make the total length of the option
126 string for the mounted file system too long.
127
128
129 EPERM
130 The calling process does not have {PRIV_SYS_MOUNT}
131 privilege and either a MNTIOC_SETTAG or MNTIOC_CLRTAG
132 call was made.
133
134
135 FILES
136 /etc/mnttab
137 Usual mount point for mnttab file system
138
139
140 /usr/include/sys/mntio.h
141 Header file that contains IOCTL definitions
142
143
144 SEE ALSO
145 mkfile(1M), mount_hsfs(1M), mount_nfs(1M), mount_pcfs(1M),
146 mount_ufs(1M), mount(1M), ioctl(2), read(2), poll(2), stat(2),
147 getmntent(3C)
148
149 WARNINGS
150 The mnttab file system provides the previously undocumented dev=xxx
151 option in the option string for each mounted file system. This is
152 provided for legacy applications that might have been using the
153 dev=information option.
154
155
156 Using dev=option in applications is strongly discouraged. The device
157 number string represents a 32-bit quantity and might not contain
158 correct information in 64-bit environments.
159
160
161 Applications requiring device number information for mounted file
162 systems should use the getextmntent(3C) interface, which functions
163 properly in either 32- or 64-bit environments.
164
165 NOTES
166 The snapshot of the mnttab information is taken any time a read(2) is
167 performed at offset 0 (the beginning) of the mnttab file. The file
168 modification time returned by stat(2) for the mnttab file is the time
169 of the last change to mounted file system information. A poll(2) system
170 call requesting a POLLRDBAND event can be used to block and wait for
171 the system's mounted file system information to be different from the
172 most recent snapshot since the mnttab file was opened.
173
174
175
176 September 8, 2015 MNTTAB(4)