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26 .TH IOCTL_IFLAGS 2 2019-11-19 "Linux" "Linux Programmer's Manual"
27 .SH NAME
28 ioctl_iflags \- ioctl() operations for inode flags
29 .SH DESCRIPTION
30 Various Linux filesystems support the notion of
31 .IR "inode flags" \(emattributes
32 that modify the semantics of files and directories.
33 These flags can be retrieved and modified using two
34 .BR ioctl (2)
35 operations:
36 .PP
37 .in +4n
38 .EX
39 int attr;
40 fd = open("pathname", ...);
42 ioctl(fd, FS_IOC_GETFLAGS, &attr); /* Place current flags
43 in \(aqattr\(aq */
44 attr |= FS_NOATIME_FL; /* Tweak returned bit mask */
45 ioctl(fd, FS_IOC_SETFLAGS, &attr); /* Update flags for inode
46 referred to by \(aqfd\(aq */
47 .EE
48 .in
49 .PP
50 The
51 .BR lsattr (1)
52 and
53 .BR chattr (1)
54 shell commands provide interfaces to these two operations,
55 allowing a user to view and modify the inode flags associated with a file.
56 .PP
57 The following flags are supported
58 (shown along with the corresponding letter used to indicate the flag by
59 .BR lsattr (1)
60 and
61 .BR chattr (1)):
62 .TP
63 .BR FS_APPEND_FL " \(aqa\(aq"
64 The file can be opened only with the
65 .B O_APPEND
66 flag.
67 (This restriction applies even to the superuser.)
68 Only a privileged process
69 .RB ( CAP_LINUX_IMMUTABLE )
70 can set or clear this attribute.
71 .TP
72 .BR FS_COMPR_FL " \(aqc\(aq"
73 Store the file in a compressed format on disk.
74 This flag is
75 .I not
76 supported by most of the mainstream filesystem implementations;
77 one exception is
78 .BR btrfs (5).
79 .TP
80 .BR FS_DIRSYNC_FL " \(aqD\(aq (since Linux 2.6.0)"
81 Write directory changes synchronously to disk.
82 This flag provides semantics equivalent to the
83 .BR mount (2)
84 .B MS_DIRSYNC
85 option, but on a per-directory basis.
86 This flag can be applied only to directories.
87 .\" .TP
88 .\" .BR FS_EXTENT_FL " \(aqe\(aq"
89 .\" FIXME Some support on ext4? (EXT4_EXTENTS_FL)
90 .TP
91 .BR FS_IMMUTABLE_FL " \(aqi\(aq"
92 The file is immutable:
93 no changes are permitted to the file contents or metadata
94 (permissions, timestamps, ownership, link count, and so on).
95 (This restriction applies even to the superuser.)
96 Only a privileged process
97 .RB ( CAP_LINUX_IMMUTABLE )
98 can set or clear this attribute.
99 .TP
100 .BR FS_JOURNAL_DATA_FL " \(aqj\(aq"
101 Enable journaling of file data on
102 .BR ext3 (5)
103 and
104 .BR ext4 (5)
105 filesystems.
106 On a filesystem that is journaling in
107 .I ordered
108 or
109 .I writeback
110 mode, a privileged
111 .RB ( CAP_SYS_RESOURCE )
112 process can set this flag to enable journaling of data updates on
113 a per-file basis.
114 .TP
115 .BR FS_NOATIME_FL " \(aqA\(aq"
116 Don't update the file last access time when the file is accessed.
117 This can provide I/O performance benefits for applications that do not care
118 about the accuracy of this timestamp.
119 This flag provides functionality similar to the
120 .BR mount (2)
121 .BR MS_NOATIME
122 flag, but on a per-file basis.
123 .\" .TP
124 .\" .BR FS_NOCOMP_FL " \(aq\(aq"
125 .\" FIXME Support for FS_NOCOMP_FL on Btrfs?
126 .TP
127 .BR FS_NOCOW_FL " \(aqC\(aq (since Linux 2.6.39)"
128 The file will not be subject to copy-on-write updates.
129 This flag has an effect only on filesystems that support copy-on-write
130 semantics, such as Btrfs.
131 See
132 .BR chattr (1)
133 and
134 .BR btrfs (5).
135 .TP
136 .BR FS_NODUMP_FL " \(aqd\(aq"
137 Don't include this file in backups made using
138 .BR dump (8).
139 .TP
140 .BR FS_NOTAIL_FL " \(aqt\(aq"
141 This flag is supported only on Reiserfs.
142 It disables the Reiserfs tail-packing feature,
143 which tries to pack small files (and the final fragment of larger files)
144 into the same disk block as the file metadata.
145 .TP
146 .BR FS_PROJINHERIT_FL " \(aqP\(aq (since Linux 4.5)"
147 .\" commit 040cb3786d9b25293b8b0b05b90da0f871e1eb9b
148 .\" Flag name was added in Linux 4.4
149 .\" FIXME Not currently supported because not in FS_FL_USER_MODIFIABLE?
150 Inherit the quota project ID.
151 Files and subdirectories will inherit the project ID of the directory.
152 This flag can be applied only to directories.
153 .TP
154 .BR FS_SECRM_FL " \(aqs\(aq"
155 Mark the file for secure deletion.
156 This feature is not implemented by any filesystem,
157 since the task of securely erasing a file from a recording medium
158 is surprisingly difficult.
159 .TP
160 .BR FS_SYNC_FL " \(aqS\(aq"
161 Make file updates synchronous.
162 For files, this makes all writes synchronous
163 (as though all opens of the file were with the
164 .BR O_SYNC
165 flag).
166 For directories, this has the same effect as the
167 .BR FS_DIRSYNC_FL
168 flag.
169 .TP
170 .BR FS_TOPDIR_FL " \(aqT\(aq"
171 Mark a directory for special treatment under the Orlov block-allocation
172 strategy.
173 See
174 .BR chattr (1)
175 for details.
176 This flag can be applied only to directories and
177 has an effect only for ext2, ext3, and ext4.
178 .TP
179 .BR FS_UNRM_FL " \(aqu\(aq"
180 Allow the file to be undeleted if it is deleted.
181 This feature is not implemented by any filesystem,
182 since it is possible to implement file-recovery mechanisms outside the kernel.
183 .PP
184 In most cases,
185 when any of the above flags is set on a directory,
186 the flag is inherited by files and subdirectories
187 created inside that directory.
188 Exceptions include
189 .BR FS_TOPDIR_FL ,
190 which is not inheritable, and
191 .BR FS_DIRSYNC_FL ,
192 which is inherited only by subdirectories.
193 .SH CONFORMING TO
194 Inode flags are a nonstandard Linux extension.
195 .SH NOTES
196 In order to change the inode flags of a file using the
197 .BR FS_IOC_SETFLAGS
198 operation,
199 the effective user ID of the caller must match the owner of the file,
200 or the caller must have the
201 .BR CAP_FOWNER
202 capability.
203 .PP
204 The type of the argument given to the
205 .BR FS_IOC_GETFLAGS
206 and
207 .BR FS_IOC_SETFLAGS
208 operations is
209 .IR "int\ *" ,
210 notwithstanding the implication in the kernel source file
211 .I include/uapi/linux/fs.h
212 that the argument is
213 .IR "long\ *" .
214 .SH SEE ALSO
215 .BR chattr (1),
216 .BR lsattr (1),
217 .BR mount (2),
218 .BR btrfs (5),
219 .BR ext4 (5),
220 .BR xfs (5),
221 .BR xattr (7),
222 .BR mount (8)