SQFSTAR - A tool to create a Squashfs filesystem from a TAR archive Sqfstar will read an uncompressed TAR archive from standard in, and it will create a Squashfs filesystem from it. If a TAR archive is compressed it should be piped through a decompressor utility and then input into Sqfstar. Sqfstar supports V7, ustar, bsdtar (libarchive), GNU tar and PAX extensions. Sparse file extensions are supported, including the "old GNU format, type S", and PAX formats, Versions 0.0, 0.1 and the current 1.0. Sqfstar supports extended attributes, and recognises the SCHILY xattr PAX extension (used by GNU tar), and the LIBARCHIVE xattr PAX extension (used by bsdtar). The Sqfstar usage info is: SYNTAX:sqfstar [OPTIONS] FILESYSTEM [list of exclude dirs/files] Filesystem compression options: -b set data block to . Default 128 Kbytes. Optionally a suffix of K or M can be given to specify Kbytes or Mbytes respectively -comp select compression Compressors available: gzip (default) lzo lz4 xz zstd -noI do not compress inode table -noId do not compress the uid/gid table (implied by -noI) -noD do not compress data blocks -noF do not compress fragment blocks -noX do not compress extended attributes -no-compression do not compress any of the data or metadata. This is equivalent to specifying -noI -noD -noF and -noX Filesystem build options: -reproducible build filesystems that are reproducible (default) -not-reproducible build filesystems that are not reproducible -mkfs-time set filesystem creation timestamp to . can be an unsigned 32-bit int indicating seconds since the epoch (1970-01-01) or a string value which is passed to the "date" command to parse. Any string value which the date command recognises can be used such as "now", "last week", or "Wed Feb 15 21:02:39 GMT 2023" -all-time set all file timestamps to . can be an unsigned 32-bit int indicating seconds since the epoch (1970-01-01) or a string value which is passed to the "date" command to parse. Any string value which the date command recognises can be used such as "now", "last week", or "Wed Feb 15 21:02:39 GMT 2023" -root-time set root directory time to . can be an unsigned 32-bit int indicating seconds since the epoch (1970-01-01) or a string value which is passed to the "date" command to parse. Any string value which the date command recognises can be used such as "now", "last week", or "Wed Feb 15 21:02:39 GMT 2023" -root-mode set root directory permissions to octal -root-uid set root directory owner to specified , can be either an integer uid or user name -root-gid set root directory group to specified , can be either an integer gid or group name -all-root make all files owned by root -force-uid set all file uids to specified , can be either an integer uid or user name -force-gid set all file gids to specified , can be either an integer gid or group name -default-mode tar files often do not store permissions for intermediate directories. This option sets the default directory permissions to octal , rather than 0755. This also sets the root inode mode -default-uid tar files often do not store uids for intermediate directories. This option sets the default directory owner to , rather than the user running Sqfstar. This also sets the root inode uid -default-gid tar files often do not store gids for intermediate directories. This option sets the default directory group to , rather than the group of the user running Sqfstar. This also sets the root inode gid -pseudo-override make pseudo file uids and gids override -all-root, -force-uid and -force-gid options -exports make the filesystem exportable via NFS -no-sparse do not detect sparse files -no-fragments do not use fragments -no-tailends do not pack tail ends into fragments -no-duplicates do not perform duplicate checking -no-hardlinks do not hardlink files, instead store duplicates Filesystem filter options: -p add pseudo file definition. The definition should be quoted -pf add list of pseudo file definitions. Pseudo file definitions in pseudo-files should not be quoted -ef list of exclude dirs/files. One per line -regex allow POSIX regular expressions to be used in exclude dirs/files -ignore-zeros allow tar files to be concatenated together and fed to Sqfstar. Normally a tarfile has two consecutive 512 byte blocks filled with zeros which means EOF and Sqfstar will stop reading after the first tar file on encountering them. This option makes Sqfstar ignore the zero filled blocks Filesystem extended attribute (xattrs) options: -no-xattrs do not store extended attributes -xattrs store extended attributes (default) -xattrs-exclude exclude any xattr names matching . is a POSIX regular expression, e.g. -xattrs-exclude '^user.' excludes xattrs from the user namespace -xattrs-include include any xattr names matching . is a POSIX regular expression, e.g. -xattrs-include '^user.' includes xattrs from the user namespace -xattrs-add add the xattr with to files. If an user xattr it will be added to regular files and directories (see man 7 xattr). Otherwise it will be added to all files. by default will be treated as binary (i.e. an uninterpreted byte sequence), but it can be prefixed with 0s, where it will be treated as base64 encoded, or prefixed with 0x, where val will be treated as hexidecimal. Additionally it can be prefixed with 0t where this encoding is similar to binary encoding, except backslashes are specially treated, and a backslash followed by 3 octal digits can be used to encode any ASCII character, which obviously can be used to encode control codes. The option can be repeated multiple times to add multiple xattrs Sqfstar runtime options: -version print version, licence and copyright message -force force Sqfstar to write to block device or file -exit-on-error treat normally ignored errors as fatal -quiet no verbose output -info print files written to filesystem -no-progress do not display the progress bar -progress display progress bar when using the -info option -percentage display a percentage rather than the full progress bar. Can be used with dialog --gauge etc. -throttle throttle the I/O input rate by the given percentage. This can be used to reduce the I/O and CPU consumption of Sqfstar -limit limit the I/O input rate to the given percentage. This can be used to reduce the I/O and CPU consumption of Sqfstar (alternative to -throttle) -processors use processors. By default will use number of processors available -mem use physical memory for caches. Use K, M or G to specify Kbytes, Mbytes or Gbytes respectively -mem-percent use physical memory for caches. Default 25% -mem-default print default memory usage in Mbytes Expert options (these may make the filesystem unmountable): -nopad do not pad filesystem to a multiple of 4K -offset skip bytes at the beginning of FILESYSTEM. Optionally a suffix of K, M or G can be given to specify Kbytes, Mbytes or Gbytes respectively. Default 0 bytes -o synonym for -offset Miscellaneous options: -fstime alternative name for mkfs-time -root-owned alternative name for -all-root -noInodeCompression alternative name for -noI -noIdTableCompression alternative name for -noId -noDataCompression alternative name for -noD -noFragmentCompression alternative name for -noF -noXattrCompression alternative name for -noX -help output this options text to stdout -h output this options text to stdout -Xhelp print compressor options for selected compressor Pseudo file definition format: "filename d mode uid gid" create a directory "filename m mode uid gid" modify filename "filename b mode uid gid major minor" create a block device "filename c mode uid gid major minor" create a character device "filename f mode uid gid command" create file from stdout of command "filename s mode uid gid symlink" create a symbolic link "filename i mode uid gid [s|f]" create a socket (s) or FIFO (f) "filename x name=val" create an extended attribute "filename l linkname" create a hard-link to linkname "filename L pseudo_filename" same, but link to pseudo file "filename D time mode uid gid" create a directory with timestamp time "filename M time mode uid gid" modify a file with timestamp time "filename B time mode uid gid major minor" create block device with timestamp time "filename C time mode uid gid major minor" create char device with timestamp time "filename F time mode uid gid command" create file with timestamp time "filename S time mode uid gid symlink" create symlink with timestamp time "filename I time mode uid gid [s|f]" create socket/fifo with timestamp time Files and directories in the TAR archive may be excluded, and both anchored and non-anchored exclude files are supported (see section 6 and examples later). Wildcards (globbing) is supported by default. Sqfstar can also by invoked by running "mksquashfs - image.sqfs -tar", if the Sqfstar link isn't available. 1. USAGE EXAMPLES ----------------- % sqfstar image.sqfs < archive.tar Create a Squashfs image from archive.tar, using defaults (gzip compression, 128K blocks). % sqfstar -comp xz -b 1M image.sqfs < archive.tar As previous, but use XZ compression and 1Mbyte block sizes. % zcat archive.tgz | sqfstar image.sqfs Create a Squashfs image from a gzip compressed tar archive. % sqfstar -root-uid 0 -root-gid 0 image.sqfs < archive.tar Tar files do not supply a definition for the root directory, and the default is to make the directory owned/group owned by the user running Sqfstar. The above command sets the ownership/group ownership to root. % sqfstar -root-mode 0755 image.sqfs < archive.tar The default permissions for the root directory is 0777 (rwxrwxrwx). The above command sets the permissions to 0755 (rwxr-xr-x). % sqfstar image.sqsh dir1/file1 dir2/file2 < archive.tar Create a Squashfs image but exclude the files "file1" and "file2". % sqfstar image.sqsh "... *.[ch]" < archive.tar Create a Squashfs image but exclude any file matching "*.[ch]" anywhere in the archive. 2. CHANGING COMPRESSION ALGORITHM AND COMPRESSION SPECIFIC OPTIONS ------------------------------------------------------------------ By default Sqfstar will compress using the GZIP compression algorithm. This algorithm offers a good trade-off between compression ratio, and memory and time taken to decompress. Squashfs also supports LZ4, LZO, XZ and ZSTD compression. LZO offers worse compression ratio than GZIP, but is faster to decompress. XZ offers better compression ratio than GZIP, but at the expense of greater memory and time to decompress (and significantly more time to compress). LZ4 is similar to LZO. ZSTD has been developed by Facebook, and aims to compress well and be fast to decompress. You should experiment with the compressors to see which is best for you. If you're not building the squashfs-tools and kernel from source, then the tools and kernel may or may not have been built with support for LZ4, LZO, XZ or ZSTD compression. The compression algorithms supported by the build of Sqfstar can be found by typing sqfstar -help. The full list of compressors available and their compression specific options are: Compressors available and compressor specific options: gzip (default) -Xcompression-level

should be 1 .. 9 (default 9) -Xwindow-size

should be 8 .. 15 (default 15) -Xstrategy strategy1,strategy2,...,strategyN Compress using strategy1,strategy2,...,strategyN in turn and choose the best compression. Available strategies: default, filtered, huffman_only, run_length_encoded and fixed lzo -Xalgorithm Where is one of: lzo1x_1 lzo1x_1_11 lzo1x_1_12 lzo1x_1_15 lzo1x_999 (default) -Xcompression-level

should be 1 .. 9 (default 8) Only applies to lzo1x_999 algorithm lz4 -Xhc Compress using LZ4 High Compression xz -Xbcj filter1,filter2,...,filterN Compress using filter1,filter2,...,filterN in turn (in addition to no filter), and choose the best compression. Available filters: x86, arm, armthumb, powerpc, sparc, ia64 -Xdict-size Use as the XZ dictionary size. The dictionary size can be specified as a percentage of the block size, or as an absolute value. The dictionary size must be less than or equal to the block size and 8192 bytes or larger. It must also be storable in the xz header as either 2^n or as 2^n+2^(n+1). Example dict-sizes are 75%, 50%, 37.5%, 25%, or 32K, 16K, 8K etc. zstd -Xcompression-level

should be 1 .. 22 (default 15) If the compressor offers compression specific options (all the compressors now have compression specific options except the deprecated lzma1 compressor) then these options are also displayed (.i.e. in the above XZ is shown with two compression specific options). The compression specific options are, obviously, specific to the compressor in question, and the compressor documentation and web sites should be consulted to understand their behaviour. In general the Sqfstar compression defaults for each compressor are optimised to give the best performance for each compressor, where what constitutes best depends on the compressor. For GZIP/XZ best means highest compression, for LZO/LZ4 best means a tradeoff between compression and (de)-compression overhead (LZO/LZ4 by definition are intended for weaker processors). 3. REDUCING CPU AND I/O USAGE ----------------------------- By default Sqfstar will use all the CPUs available to compress and create the filesystem, and will read from the TAR archive and write to the output filesystem as fast as possible. This maximises both CPU usage and I/O. Sometimes you don't want Sqfstar to use all CPU and I/O bandwidth. For those cases Sqfstar supports two complementary options, -processors and -throttle. The -processors option can be used to reduce the number of parallel compression threads used by Sqfstar. Reducing this to 1 will create the minimum number of threads, and this will reduce CPU usage, and that in turn will reduce I/O (because CPUs are normally the bottleneck). The -throttle option reduces the speed Sqfstar reads from the TAR archive. The value is a percentage (obviously from 1 - 100), and 50 will reduce the read rate by half (the read thread will spend half its time idling), and 75 by three quarters. Reducing the speed of I/O will also reduce the CPU usage as there is insufficient data rate to use all cores. Which option should you use? Both will effectively reduce CPU and I/O in normal cases where intensive use is being made of both I/O and CPUs. But in edge cases there can be an imbalance where reducing one has no effect, or it can't be reduced any further. For instance when there is only 1 or 2 cores available, setting -processors to the minimum of 1 may still use too much CPU. Additionally if your input source is slow Sqfstar may still max it out with -processors set to the minimum of 1. In this case you can use -throttle in addition to -processors or on its own. 4. CHANGING GLOBAL COMPRESSION DEFAULTS USED IN SQFSTAR ------------------------------------------------------- There are a large number of options that can be used to control the compression in Sqfstar. By and large the defaults are the most optimum settings and should rarely need to be changed. Note, this does not apply to the block size, increasing the block size from the default of 128 Kbytes will increase compression (especially for the XZ and ZSTD compressors) and should increase I/O performance too. However, a block size of greater than 128 Kbytes may increase latency in certain cases (where the filesystem contains lots of fragments, and no locality of reference is observed). For this reason the block size default is configured to the less optimal 128 Kbytes. Users should experiment with 256 Kbyte sizes or above. The -b option allows the block size to be selected, both "K" and "M" postfixes are supported, this can be either 4K, 8K, 16K, 32K, 64K, 128K, 256K, 512K or 1M bytes. The -noI, -noD, -noF and -noX options can be used to force Sqfstar to not compress inodes/directories, data, fragments and extended attributes respectively. Giving all options generates an uncompressed filesystem. The -no-fragments option tells Sqfstar to not generate fragment blocks. A fragment block consists of multiple small files (all smaller than the block size) packed and compressed together. This produces much better compression than storing and compressing these files separately. It also typically improves I/O as multiple files in the same directory are read at the same time. You don't want to enable this option unless you fully understand the effects. The -no-tailends option tells Sqfstar to not pack file tailends into fragment blocks. Normally a file will not be a multiple of the block size, and so there were always be a tail which doesn't fit fully into a data block. This tailend is by default packed into fragment blocks. Enabling this option will reduce compression. The -no-duplicates option tells Sqfstar to not check the files being added to the filesystem for duplicates. This can result in quicker filesystem generation although obviously compression will suffer badly if there is a lot of duplicate files. 5. SPECIFYING THE UIDs/GIDs USED IN THE FILESYSTEM -------------------------------------------------- By default files in the generated filesystem use the ownership of the file stored in the TAR archive. TAR archives depending on the TAR format stores ownership in two ways. The early V7 format only stored a numeric UID and GID. If Sqfstar is reading a V7 archive these are used. Later ustar and PAX archives can also store a string user name and group name. If these are present and are recognised by the system (i.e. can be mapped to a UID and GID), their UID and GID is used. If a user name or group name is not recognised by the system, the numeric UID or GID is used. The -all-root option forces all file UIDs/GIDs in the generated Squashfs filesystem to be root. This allows root owned filesystems to be built without root access on the host machine. The "-force-uid value" option forces all files in the generated Squashfs filesystem to be owned by value, where value can either be a user name or a numeric UID. The "-force-gid value" option forces all files in the generated Squashfs filesystem to be group owned by value, where value can be either a group name or a numeric GID. 6. EXCLUDING FILES FROM THE FILESYSTEM -------------------------------------- Sqfstar can exclude files from the TAR archive, so that they don't appear in the Squashfs filesystem. Exclude files can be directly specified on the command line (immediately after the FILESYSTEM argument), or the -ef option can be used to specify an exclude file, with one exclude file per line. Exclude files by default use wildcard matching (globbing) and can match on more than one file (if wildcards are used). Regular expression matching can be used instead by specifying the -regex option. In most cases wildcards should be used rather than regular expressions because wildcard matching behaviour is significantly easier to understand! In addition to wildcards/regex expressions, exclude files can be "anchored" or "non-anchored". An anchored exclude is one which matches from the root of the directory and nowhere else, a non-anchored exclude matches anywhere. For example given the directory hierarchy "a/b/c/a/b", the anchored exclude "a/b" will match "a/b" at the root of the directory hierarchy, but it will not match the "/a/b" sub-directory within directory "c", whereas a non-anchored exclude would. A couple of examples should make this clearer. Anchored excludes 1. sqfstar image.sqsh 'test/*.gz' < archive.tar Exclude all files matching "*.gz" in the top level directory "test". 2. sqfstar image.sqsh '*/[Tt]est/example*' < archive.tar Exclude all files beginning with "example" inside directories called "Test" or "test", that occur inside any top level directory. Using extended wildcards, negative matching is also possible. 3. sqfstar image.sqsh 'test/!(*data*).gz' < archive.tar Exclude all files matching "*.gz" in top level directory "test", except those with "data" in the name. Non-anchored excludes By default excludes match from the top level directory, but it is often useful to exclude a file matching anywhere in the source directories. For this non-anchored excludes can be used, specified by pre-fixing the exclude with "...". Examples: 1. sqfstar image.sqsh '... *.gz' < archive.tar Exclude files matching "*.gz" anywhere in the source directories. For example this will match "example.gz", "test/example.gz", and "test/test/example.gz". 2. sqfstar image.sqsh '... [Tt]est/*.gz' < archive.tar Exclude files matching "*.gz" inside directories called "Test" or "test" that occur anywhere in the source directories. Again, using extended wildcards, negative matching is also possible. 3. sqfstar image.sqsh '... !(*data*).gz' < archive.tar Exclude all files matching "*.gz" anywhere in the source directories, except those with "data" in the name. 7. FILTERING AND ADDING EXTENDED ATTRIBUTES (XATTRs) ---------------------------------------------------- Sqfstar has a number of options which allow extended attributes (xattrs) to be filtered from the TAR archive or added to the created Squashfs filesystem. The -no-xattrs option removes any extended attributes which may exist in the TAR archive, and creates a filesystem without any extended attributes. The -xattrs-exclude option specifies a regular expression (regex), which removes any extended attribute that matches the regular expression from all files. For example the regex '^user.' will remove all User extended attributes. The -xattrs-include option instead specifies a regular expression (regex) which includes any extended attribute that matches, and removes anything that does't match. For example the regex '^user.' will only keep User extended attributes and anything else will be removed. Sqfstar also allows you to add extended attributes to files in the Squashfs filesystem using the -xattrs-add option. This option takes an xattr name and value pair separated by the '=' character. The extended attribute name can be any valid name and can be in the namespaces security, system, trusted, or user. User extended attributes are added to files and directories (see man 7 xattr for explanation), and the others are added to all files. The extended attribute value by default will be treated as binary (i.e. an uninterpreted byte sequence), but it can be prefixed with 0s, where it will be treated as base64 encoded, or prefixed with 0x, where it will be treated as hexidecimal. Obviously using base64 or hexidecimal allows values to be used that cannot be entered on the command line such as non-printable characters etc. But it renders the string non-human readable. To keep readability and to allow non-printable characters to be entered, the 0t prefix is supported. This encoding is similar to binary encoding, except backslashes are specially treated, and a backslash followed by three octal digits can be used to encode any ASCII character, which obviously can be used to encode non-printable values. The following four command lines are equivalent sqfstar -xattrs-add "user.comment=hello world" image.sqfs sqfstar -xattrs-add "user.comment=0saGVsbG8gd29ybGQ=" image.sqfs sqfstar -xattrs-add "user.comment=0x68656c6c6f20776f726c64" sqfstar -xattrs-add "user.comment=0thello world" image.sqfs Obviously in the above example there are no non-printable characters and so the 0t prefixed string is identical to the first line. The following three command lines are identical, but where the space has been replaced by the non-printable NUL '\0' (null character). sqfstar -xattrs-add "user.comment=0thello\000world" image.sqfs sqfstar -xattrs-add "user.comment=0saGVsbG8Ad29ybGQ=" image.sqfs sqfstar -xattrs-add "user.comment=0x68656c6c6f00776f726c64" image.sqsh 8. PSEUDO FILE SUPPORT ---------------------- Sqfstar supports pseudo files, these allow files, directories, character devices, block devices, fifos, symbolic links, hard links and extended attributes to be specified and added to the Squashfs filesystem being built, rather than requiring them to be present in the TAR archive. This, for example, allows device nodes to be added to the filesystem without requiring root access. Pseudo files also support "dynamic pseudo files" and a modify operation. Dynamic pseudo files allow files to be dynamically created when Sqfstar is run, their contents being the result of running a command or piece of shell script. The modifiy operation allows the mode/uid/gid of an existing file in the source filesystem to be modified. Two Sqfstar options are supported, -p allows one pseudo file to be specified on the command line, and -pf allows a pseudo file to be specified containing a list of pseduo definitions, one per line. 8.1 CREATING A DYNAMIC FILE --------------------------- Pseudo definition Filename f mode uid gid command mode is the octal mode specifier, similar to that expected by chmod. uid and gid can be either specified as a decimal number, or by name. command can be an executable or a piece of shell script, and it is executed by running "/bin/sh -c command". The stdout becomes the contents of "Filename". Examples: Running a basic command ----------------------- /somedir/dmesg f 444 root root dmesg creates a file "/somedir/dmesg" containing the output from dmesg. Executing shell script ---------------------- RELEASE f 444 root root \ if [ ! -e /tmp/ver ]; then \ echo 0 > /tmp/ver; \ fi; \ ver=`cat /tmp/ver`; \ ver=$((ver +1)); \ echo $ver > /tmp/ver; \ echo -n `cat /tmp/release`; \ echo "-dev #"$ver `date` "Build host" `hostname` Creates a file RELEASE containing the release name, date, build host, and an incrementing version number. The incrementing version is a side-effect of executing the shell script, and ensures every time Sqfstar is run a new version number is used without requiring any other shell scripting. The above example also shows that commands can be split across multiple lines using "\". Obviously as the script will be presented to the shell as a single line, a semicolon is need to separate individual shell commands within the shell script. Reading from a device (or fifo/named socket) -------------------------------------------- input f 444 root root dd if=/dev/sda1 bs=1024 count=10 Copies 10K from the device /dev/sda1 into the file input. Ordinarily Sqfstar given a device, fifo, or named socket will place that special file within the Squashfs filesystem, the above allows input from these special files to be captured and placed in the Squashfs filesystem. 8.2 CREATING A BLOCK OR CHARACTER DEVICE ---------------------------------------- Pseudo definition Filename type mode uid gid major minor Where type is either b - for block devices, and c - for character devices mode is the octal mode specifier, similar to that expected by chmod. uid and gid can be either specified as a decimal number, or by name. For example: /dev/chr_dev c 666 root root 100 1 /dev/blk_dev b 666 0 0 200 200 creates a character device "/dev/chr_dev" with major:minor 100:1 and a block device "/dev/blk_dev" with major:minor 200:200, both with root uid/gid and a mode of rw-rw-rw. 8.3 CREATING A DIRECTORY ------------------------ Pseudo definition Filename d mode uid gid mode is the octal mode specifier, similar to that expected by chmod. uid and gid can be either specified as a decimal number, or by name. For example: /pseudo_dir d 666 root root creates a directory "/pseudo_dir" with root uid/gid and mode of rw-rw-rw. 8.4 CREATING A SYMBOLIC LINK ---------------------------- Pseudo definition Filename s mode uid gid symlink uid and gid can be either specified as a decimal number, or by name. Note mode is ignored, as symlinks always have "rwxrwxrwx" permissions. For example: symlink s 0 root root example Creates a symlink "symlink" to file "example" with root uid/gid. 8.5 CREATING HARD LINKS (FILE REFERENCES) ----------------------------------------- The "f" Pseudo definition allows a regular file to be created from the output of a command (or shell). Often this is used to reference a file outside the source directories by executing "cat", e.g. README f 0555 0 0 cat /home/phillip/latest-version/README Because this is a quite frequent use of the definition, an alternative faster "File reference" or Hard Link Pseudo definition exists: README l /home/phillip/latest-version/README Will create a reference to "/home/phillip/latest-version/README", and obviously the timestamp/mode and owership will be used. The definition also can be used to create additional references to files within the source directories. For instance if "phillip/latest/README" was a file being added to the filesystem, then README l phillip/latest/README Will create a Hard Link (and increment the nlink count on the inode). In both cases, the path to the file being referenced is the system filesystem path, and can be absolute (prefixed with /), or relative to the current working directory. There is an additional 'L' Pseudo definition, which closes a loophole in the above 'l' definition. The 'l' Pseudo definition cannot create references or Hard Links to files created by Pseudo definitions, because by definition they do not exist in the system filesystem. with 'L' the referenced file is expected to be a Pseudo file, and in this case the path is taken to be from the root of the Squashfs filesystem being created, e.g. char-dev c 0555 0 0 1 2 link L char-dev Will create a Hard Link named "link" to the character device called "char-dev" created by the previous Pseudo definition. 8.6 CREATING SOCKETS/FIFOS -------------------------- Pseudo definition filename i mode uid gid [s|f] To create a Unix domain socket, 's' should be used, i.e. filename i 0777 root root s and to create a FIFO, 'f' should be used, i.e. filename i 0777 root root f 8.7 ADDING EXTENDED ATTRIBUTES TO FILES --------------------------------------- Pseudo definition filename x name=val Will add the extended attribute to with contents. See Section 7 for a description of the formats supported. 8.8 MODIFYING ATTRIBUTES OF AN EXISTING FILE -------------------------------------------- Pseudo definition Filename m mode uid gid mode is the octal mode specifier, similar to that expected by chmod. uid and gid can be either specified as a decimal number, or by name. For example: dmesg m 666 root root Changes the attributes of the file "dmesg" in the filesystem to have root uid/gid and a mode of rw-rw-rw, overriding the attributes obtained from the TAR archive. 9. EXTENDED PSEUDO FILE DEFINITIONS WITH TIMESTAMPS --------------------------------------------------- The Pseudo file definitions described above do not allow the timestamp of the created file to be specified, and the files will be timestamped with the current time. Extended versions of the Pseudo file definitions are supported which take a timestamp. These are distinquished from the previous definitions by using an upper-case type character. For example the "D" definition is identical to the "d" definition, but it takes a timestamp. The list of extended definitions are: filename F time mode uid gid command filename D time mode uid gid filename B time mode uid gid major minor filename C time mode uid gid major minor filename S time mode uid gid symlink filename I time mode uid gid [s|f] filename M time mode uid gid can be either an unsigned decimal integer (which represents the seconds since the epoch of 1970-01-01 00:00 UTC), or a "date string" which is parsed and converted into an integer since the epoch, by calling the "date" command. Because most date strings have spaces, they will need to be quoted, and if entered on the command line, these quotes will need to be protected from the shell by backslashes, i.e. % sqfstar img.sqfs -p "file D \"1 jan 1980\" 0777 phillip phillip" < archive.tar Obviously anything "date" accepts as a valid string can be used, such as "yesterday", "last week" etc. 10. MISCELLANEOUS OPTIONS ------------------------ The -info option displays the files/directories as they are compressed and added to the filesystem. The original uncompressed size of each file is printed, along with DUPLICATE if the file is a duplicate of a file in the filesystem. The -nopad option informs Sqfstar to not pad the filesystem to a 4K multiple. This is performed by default to enable the output filesystem file to be mounted by loopback, which requires files to be a 4K multiple. If the filesystem is being written to a block device, or is to be stored in a bootimage, the extra pad bytes are not needed.