1SG_WR_MODE(8) SG3_UTILS SG_WR_MODE(8)
2
6 sg_wr_mode - write mode page
7
9 sg_wr_mode [--contents=H,H...] [--dbd] [--force] [--help] [--len=10|6]
10 [--mask=M,M...] [--page=PG[,SPG]] [--save] [--verbose] [--version]
11 DEVICE
12
14 Writes a modified mode page to DEVICE. Uses the SCSI MODE SENSE (6 or
15 10 byte variant) command to fetch the existing mode data which includes
16 a mode page (or subpage). It then combines that with the contents,
17 potentially masked, and writes the modified mode page with the SCSI
18 MODE SELECT (6 or 10 byte variant) command. This utility does not mod‐
19 ify the block descriptor(s); if any block descriptors are fetched by
20 the MODE SENSE command then the same block descriptors are written back
21 with the following MODE SELECT command.
22 If a contents argument is not given then the various components (i.e.
24 header, block descriptor(s) and mode page) of the "current" values of
25 the existing mode page are printed out. In this case the mode page is
26 not altered on the device.
27 If the contents are specified, and a mask is not specified, then the
29 contents must match the existing mode page in various aspects unless
30 the --force option is given. These include length, mode page code and
31 subpage code if applicable. If all is well then the contents string is
32 written to DEVICE as the new mode page.
33 If both contents and mask strings are specified then only bit positions
35 in the contents corresponding to set bits in the mask are taken while
36 the existing mode page supplies bit positions corresponding to clear
37 bits. When a mask is given then the mask and/or the contents may be
38 shorter than the existing mode page. If the mask is shorter than the
39 contents then the remaining bytes are taken from the contents. If the
40 contents are shorter than the existing mode page then the remaining
41 bytes are taken from the existing mod page.
42 The force option allows the contents string to be written as the new
44 mode page without any prior checks on the existing mode page. This
45 should only be required for vendor specific mode pages. The existing
46 mode data is ignored apart from the block descriptors which can be sup‐
47 pressed with the --dbd option if need be.
48 Changing individual fields in a mode page is probably more easily done
50 with the sdparm utility. Fields can be identified by acronym or by a
51 numerical descriptor.
52
54 Arguments to long options are mandatory for short options as well.
55 -c, --contents=H,H...
57 where H,H... is a string of comma separated hex numbers each of
58 which should resolve to a byte value (i.e. 0 to ff inclusive). A
59 (single) space separated string of hex numbers is also allowed
60 but the list needs to be in quotes. This is the new contents of
61 the mode page to be written to DEVICE, potentially filtered by
62 the mask string.
63 -c, --contents=-
65 reads contents string from stdin. The hex numbers in the string
66 may be comma, space, tab or linefeed (newline) separated. If a
67 line contains "#" then the remaining characters on that line are
68 ignored. Otherwise each non separator character should resolve
69 to a byte value (i.e. 0 to ff inclusive). This forms the new
70 contents of the mode page to be written to DEVICE, potentially
71 filtered by the mask string.
72 -d, --dbd
74 disable block descriptors (DBD flag in cdb). Some device types
75 include block descriptors in the mode data returned by a MODE
76 SENSE command. If so the same block descriptors are written by
77 the MODE SELECT command. This option instructs the MODE SENSE
78 command not to return any block descriptors. This would be a
79 sensible default for this utility apart from the fact that not
80 all SCSI devices support the DBD bit in the cdb.
81 -f, --force
83 force the contents string to be taken as the new mode page, or
84 at least doesn't do checks on the existing mode page. Note that
85 DEVICE may still reject the new contents for the mode page. Can‐
86 not be given with the --mask=M,M... option.
87 -h, --help
89 output the usage message then exit.
90 -l, --len=10 | 6
92 length of the SCSI commands (cdb) sent to DEVICE. The default is
93 10 so 10 byte MODE SENSE and MODE SELECT commands are issued.
94 Some old devices don't support the 10 byte variants hence this
95 option.
96 -m, --mask=M,M...
98 where M,M... is a string of comma separated hex numbers each of
99 which should resolve to a byte value (i.e. 0 to ff inclusive). A
100 (single) space separated string of hex numbers is also allowed
101 but the list needs to be in quotes. The mask chooses (bit by
102 bit) whether the new mode page comes from the contents (mask bit
103 set) or from the existing mode page (mask bit clear). If the
104 mask string is shorter than the contents string then the remain‐
105 ing bytes are taken from the contents string. If the contents
106 string is shorter than the existing mode page then the remaining
107 bytes are taken from the existing mode page (i.e. they are left
108 unaltered).
109 -p, --page=PG
111 where PG is the page code value to fetch and modify. The page
112 code is in hex and should be between 0 and 3e inclusive. Notice
113 that page code 3f to fetch all mode pages is disallowed.
114 -p, --page=PG,SPG
116 where PG is the page code value and SPG is the subpage code
117 value to fetch and modify. Both values are in hex. The subpage
118 code should be between 0 and fe inclusive. Notice that subpage
119 code ff to fetch all mode subpages (for a given mode page or all
120 mode pages in the case of 3f,ff) is disallowed.
121 -s, --save
123 changes the "saved" mode page when MODE SELECT is successful. By
124 default (i.e. when --save is not used) only the "current" mode
125 page values are changed when MODE SELECT is successful. In this
126 case the new mode page will stay in effect until the device is
127 reset (e.g. power cycled). When it restarts the "saved" values
128 for the mode page will be re-instated. So to make changes per‐
129 manent use the --save option.
130 -v, --verbose
132 increase the level of verbosity, (i.e. debug output).
133 -V, --version
135 print the version string and then exit.
136
138 This utility does not check whether the contents string is trying to
139 modify parts of the mode page which are changeable. The device should
140 do that and if some part is not changeable then it should report:
141 "Invalid field in parameter list".
142 Some mode pages are not savable. If so an attempt to use the --save
144 option should cause an error to be reported from the device: "Illegal
145 field in cdb".
146 The device is required to do various checks before it accepts a new
148 mode page. If these checks fail then the mode page is not altered and
149 either a "parameter list length error" or an "invalid field in parame‐
150 ter list" error is returned by the device in the sense data.
151 The recommended way to modify a mode page is to read it with a MODE
153 SENSE, modify some part of it then write it back to the device with a
154 MODE SELECT command. For example, reading an existing mode page can be
155 accomplished with 'sg_modes -p=1a -r /dev/sdb > mp_1a.txt' (the power
156 condition mode page). The mp_1a.txt file can be edited and then used as
157 the contents string to this utility (e.g. 'sg_wr_mode -p 1a -s -c -
158 /dev/sdb < mp_1a.txt').
159 Two fields differ between what is read from the device with MODE SENSE
161 and what is written to the device with MODE SELECT: the mode data
162 length is reserved (i.e. zero(es)) in a MODE SELECT command while the
163 PS bit ((sub)page byte 0 bit 7) in each mode (sub)page is reserved
164 (zero) in a MODE SELECT command. The PS bit given in the contents
165 string is zeroed unless the --force option is selected.
166
168 This utility can be used together with the sg_modes utility. To
169 re-instate the default mode page values (i.e. the mode page values cho‐
170 sen by the manufacturer of the device) as both the current and saved
171 mode page values the following sequence could be used:
172 $ sg_modes --control=2 --page=1a -r /dev/sda > t
174 $ sg_wr_mode --page=1a --contents=- --save /dev/sda < t
175 Next is an example of using a mask to modify the "idle condition
177 counter" of the "power condition" mode page (0x1a) from 0x28 to 0x37.
178 Note that the change is not saved so the "idle condition counter" will
179 revert to 0x28 after the next power cycle. The output from sg_modes is
180 abridged.
181 $ sg_modes --page=1a /dev/hdc
183 >> Power condition (mmc), page_control: current
184 00 1a 0a 00 03 00 00 00 28 00 00 01 2c
185 $ sg_wr_mode -p 1a -c 0,0,0,0,0,0,0,37 -m 0,0,0,0,0,0,0,ff /dev/hdc
187 $ sg_modes -p 1a /dev/hdc
189 >> Power condition (mmc), page_control: current
190 00 1a 0a 00 03 00 00 00 37 00 00 01 2c
191
193 The exit status of sg_wr_mode is 0 when it is successful. Otherwise see
194 the sg3_utils(8) man page.
195
197 Written by Douglas Gilbert.
198
200 Report bugs to <dgilbert at interlog dot com>.
201
203 Copyright © 2004-2009 Douglas Gilbert
204 This software is distributed under a FreeBSD license. There is NO war‐
205 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
206 POSE.
207
209 sdparm(sdparm), sg_modes(sg3_utils), sginfo(sg3_utils)
210sg3_utils-1.27 April 2009 SG_WR_MODE(8)