1LOSETUP(8) MAINTENANCE COMMANDS LOSETUP(8)
2
6 losetup - set up and control loop devices
7
9 Get info:
10 losetup loopdev
12 losetup -a
14 losetup -j file [-o offset]
16 Delete loop:
18 losetup -d loopdev...
20 Print name of first unused loop device:
22 losetup -f
24 Setup loop device:
26 losetup [{-e|-E} encryption] [-o offset] [--sizelimit limit]
28 [-p pfd] [-r] {-f[--show]|loopdev} file
29 Resize loop device:
31 losetup -c loopdev
33
35 losetup is used to associate loop devices with regular files or block
36 devices, to detach loop devices and to query the status of a loop
37 device. If only the loopdev argument is given, the status of the corre‐
38 sponding loop device is shown.
39 Encryption
42 It is possible to specify transfer functions (for encryption/decryption
43 or other purposes) using one of the -E and -e options. There are two
44 mechanisms to specify the desired encryption: by number and by name. If
45 an encryption is specified by number then one has to make sure that the
46 Linux kernel knows about the encryption with that number, probably by
47 patching the kernel. Standard numbers that are always present are 0 (no
48 encryption) and 1 (XOR encryption). When the cryptoloop module is
49 loaded (or compiled in), it uses number 18. This cryptoloop module
50 will take the name of an arbitrary encryption type and find the module
51 that knows how to perform that encryption.
52
54 -a, --all
55 show status of all loop devices
56 -c, --set-capacity loopdev
58 force loop driver to reread size of the file associated with the
59 specified loop device
60 -d, --detach loopdev...
62 detach the file or device associated with the specified loop
63 device(s)
64 -e, -E, --encryption encryption_type
66 enable data encryption with specified name or number
67 -f, --find
69 find the first unused loop device. If a file argument is
70 present, use this device. Otherwise, print its name
71 -h, --help
73 print help
74 -j, --associated file
76 show status of all loop devices associated with given file
77 -o, --offset offset
79 the data start is moved offset bytes into the specified file or
80 device
81 --sizelimit limit
83 the data end is set to no more than sizelimit bytes after the
84 data start
85 -p, --pass-fd num
87 read the passphrase from file descriptor with number num instead
88 of from the terminal
89 -r, --read-only
91 setup read-only loop device
92 --show print device name if the -f option and a file argument are
94 present.
95 The short form of this option (-s) is deprecated. This short
97 form could be in collision with Loop-AES implementation where
98 the same option is used for --sizelimit.
99 -v, --verbose
101 verbose mode
102
105 losetup returns 0 on success, nonzero on failure. When losetup displays
106 the status of a loop device, it returns 1 if the device is not config‐
107 ured and 2 if an error occurred which prevented losetup from determin‐
108 ing the status of the device.
109
112 /dev/loop0, /dev/loop1, ... loop devices (major=7)
113
115 If you are using the loadable module you must have the module loaded
116 first with the command
117 # modprobe loop
119 Maybe also encryption modules are needed.
121 # modprobe des # modprobe cryptoloop
123 The following commands can be used as an example of using the loop
125 device.
126 # dd if=/dev/zero of=/file bs=1k count=100
128 # losetup -e des /dev/loop0 /file
129 Password:
130 Init (up to 16 hex digits):
131 # mkfs -t ext2 /dev/loop0 100
132 # mount -t ext2 /dev/loop0 /mnt
133 ...
134 # umount /dev/loop0
135 # losetup -d /dev/loop0
136 If you are using the loadable module you may remove the module with the
138 command
139 # rmmod loop
141
143 DES encryption is painfully slow. On the other hand, XOR is terribly
144 weak.
145 Cryptoloop is deprecated in favor of dm-crypt. For more details see
147 cryptsetup(8).
148
150 The losetup command is part of the util-linux-ng package and is avail‐
151 able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
152Linux 2003-07-01 LOSETUP(8)