lsfd - Man Page

list file descriptors


lsfd [option]


lsfd is intended to be a modern replacement for lsof(8) on Linux systems. Unlike lsof, lsfd is specialized to Linux kernel; it supports Linux specific features like namespaces with simpler code. lsfd is not a drop-in replacement for lsof; they are different in the command line interface and output formats.

lsfd uses Libsmartcols for output formatting and filtering. See the description of --output option for customizing the output format, and --filter option for filtering.


-l,  --threads

List in threads level.

-J,  --json

Use JSON output format.

-n,  --noheadings

Don’t print headings.

-o,  --output list

Specify which output columns to print. See the Output Columns section for details of available columns.

The default list of columns may be extended if list is specified in the format +list (e.g., lsfd -o +DELETED).

-r,  --raw

Use raw output format.


Don’t truncate text in columns.

-p,  --pid pids

Collect information only for specified processes. pids is a list of pids. A comma or whitespaces can be used as separators. You can use this option with pidof(1). See Filter Examples.

Both -Q option with an expression including PID, e.g. -Q (PID == 1), and -p option, e.g. -p 1, may print the same output but using -p option is much more efficient because -p option works at a much earlier stage of processing than the -Q option.

-Q,  --filter expr

Print only the files matching the condition represented by the expr. See also Filter Examples.

-C,  --counter label:filter_expr

Define a custom counter used in --summary output. lsfd makes a counter named label. During collect information, lsfd counts files matching filter_expr, and stores the counted number to the counter named label. lsfd applies filters defined with --filter options before counting; files excluded by the filters are not counted.

See Filter Expression about filter_expr. label should not include { nor :. You can define multiple counters by specifying this option multiple times.

See also Counter Examples.


This option controls summary lines output. The optional argument when can be only, append or never. If the when argument is omitted, it defaults to only.

The summary reports counters. A counter consists of a label and an integer value.  --counter is the option for defining a counter.  If a user defines no counter, lsfd uses the definitions of pre-defined built-in counters (default counters) to make the summary output.

CAUTION: Using --summary and --json may make the output broken. Only combining --summary=only and --json is valid.


Dump the internal data structure for the filter and exit. This is useful only for lsfd developers.


Dump the definition of counters used in --summary output.

-h,  --help

Display help text and exit.

-V,  --version

Print version and exit.

Output Columns

Each column has a type. Types are surround by < and >.

CAUTION: The names and types of columns are not stable yet. They may be changed in the future releases.

ASSOC <string>

Association between file and process.

BLKDRV <string>

Block device driver name resolved by /proc/devices.

CHRDRV <string>

Character device driver name resolved by /proc/devices.

COMMAND <string>

Command of the process opening the file.

DELETED <boolean>

Reachability from the file system.

DEV <string>

ID of the device containing the file.

DEVTYPE <string>

Device type (blk, char, or nodev).

FD <number>

File descriptor for the file.

FLAGS <string>

Flags specified when opening the file.

FUID <number>

User ID number of the file’s owner.

INODE <number>

Inode number.

KTHREAD <boolean>

Whether the process is a kernel thread or not.

MAJ:MIN <string>

Device ID for special, or ID of device containing file.

MAPLEN <number>

Length of file mapping (in page).

MISCDEV <string>

Misc character device name resolved by /proc/misc.

MNTID <number>

Mount ID.

MODE <string>

Access mode (rwx).

NAME <string>

Name of the file.

NLINK <number>

Link count.

OWNER <string>

Owner of the file.

PARTITION <string>

Block device name resolved by /proc/partition.

PID <number>

PID of the process opening the file.

POS <number>

File position.

PROTONAME <string>

Protocol name.

RDEV <string>

Device ID (if special file).

SIZE <number>

File size.

SOURCE <string>

File system, partition, or device containing the file.

TID <number>

Thread ID of the process opening the file.

TYPE <string>

File type.

UID <number>

User ID number.

USER <string>

User of the process.

Filter Expression

lsfd evaluates the expression passed to --filter option every time before printing a file line. lsfd prints the line only if the result of evaluation is true.

An expression consists of column names, literals and, operators like: DELETED, (PID == 1), (NAME == "/etc/passwd"), (PID == 1) && DELETED. DELETED, PID, and NAME are column names in the example. 1 and "/etc/passwd" are literals. == and && are operators.

Before evaluation, lsfd substitutes column names in the given expression with actual column values in the line. There are three different data types: boolean, string, and number.  For columns with a boolean type, the value can be stand-alone.  For string and number values, the value must be an operand of an operator, for example, (PID == 1). See the "Output Columns" about the types of columns.

Literal is for representing a value directly. See BOOLLIT, STRLIT, and NUMLIT. Different data types have different literal syntax.

An operator works with one or two operand(s). An operator has an expectation about the data type(s) of its operands. Giving an unexpected data type to an operator causes a syntax error.

Operators taking two operands are and, or, eq, ne, le, lt, ge, gt, =~, !~. Alphabetically named operators have C-language flavored aliases: &&, ||, ==, !=, <, , >=, and >.

! is the only operator that takes one operand.

eq, ne, and their aliases expect operands have the same data type. Applying these operators return a boolean.

and, or, not and their aliases expect operands have bool data type. Applying these operators return a boolean.

lt, le, gt, ge, and their aliases expect operands have number data types. Applying these operators return a boolean.

=~ is for regular expression matching; if a string at the right side matches a regular expression at the left side, the result is true. The right side operand must be a string literal. See STRLIT about the syntax.

!~ is a short-hand version of not (STR =~ PAT); it inverts the result of =~.


The current implementation does not define precedences within operators.  Use ( and ) explicitly for grouping the sub-expressions if your expression uses more than two operators.

About number typed values, the filter engine supports only non-negative integers.

Semi-formal syntax




COLUMN <boolean> | BOOLLIT | ( BOOLEXP )








COLUMN <string> | STRLIT


COLUMN <number> | NUMLIT


true | false


( [^\] | \\ | \' | \" )*


' CHARS ' | " CHARS "


[1-9][0-9]* | 0




== | eq | != | ne




&& | and |  || | or




< | lt | <= | le | > | gt | >= | ge




=~ | !~

Filter Examples

lsfd has few options for filtering. In most of cases, what you should know is -Q (or --filter) option.  Combined with -o (or --output) option, you can customize the output as you want.

List files associated with PID 1 and PID 2 processes:

# lsfd -Q '(PID == 1) or (PID == 2)'

Do the same in an alternative way:

# lsfd -Q '(PID == 1) || (PID == 2)'

Do the same in a more efficient way:

# lsfd --pid 1,2

Whitescapes can be used instead of a comma:

# lsfd --pid '1 2'

Utilize pidof(1) for list the files associated with "firefox":

# lsfd --pid "$(pidof firefox)"

List the 1st file descriptor opened by PID 1 process:

# lsfd -Q '(PID == 1) and (FD == 1)'

Do the same in an alternative way:

# lsfd -Q '(PID == 1) && (FD == 1)'

List all running executables:

# lsfd -Q 'ASSOC == "exe"'

Do the same in an alternative way:

# lsfd -Q 'ASSOC eq "exe"'

Do the same but print only file names:

# lsfd -o NAME -Q 'ASSOC eq "exe"' | sort -u

List deleted files associated to processes:

# lsfd -Q 'DELETED'

List non-regular files:

# lsfd -Q 'TYPE != "REG"'

List block devices:

# lsfd -Q 'DEVTYPE == "blk"'

Do the same with TYPE column:

# lsfd -Q 'TYPE == "BLK"'

List files including "dconf" directory in their names:

# lsfd -Q 'NAME =~ ".\*/dconf/.*"'

List files opened in a QEMU virtual machine:

# lsfd -Q '(COMMAND =~ ".\*qemu.*") and (FD >= 0)'

Hide files associated to kernel threads:

# lsfd -Q '!KTHREAD'

Counter Examples

Report the numbers of netlink socket descriptors and unix socket descriptors:

# lsfd --summary=only \
        -C 'netlink sockets':'(NAME =~ "NETLINK:.*")' \
        -C 'unix sockets':'(NAME =~ "UNIX:.*")'
   57 netlink sockets
 1552 unix sockets

Do the same but print in JSON format:

# lsfd --summary=only --json \
        -C 'netlink sockets':'(NAME =~ "NETLINK:.*")' \
        -C 'unix sockets':'(NAME =~ "UNIX:.*")'
   "lsfd-summary": [
         "value": 15,
         "counter": "netlink sockets"
         "value": 798,
         "counter": "unix sockets"


The lsfd command is part of the util-linux package since v2.38.


Masatake YAMATO, Karel Zak

See Also

lsof(8) pidof(1) proc(5)

Reporting Bugs

For bug reports, use the issue tracker at


The lsfd command is part of the util-linux package which can be downloaded from Linux Kernel Archive.


2022-08-04 util-linux 2.38.1