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+# lsof(8)
+
+```markdown
+lsof
+  -r <s> ..... repeatedly execute command ervery <s> seconds
+  -a ......... AND slection filters instead ORing (OR: default)
+  -p <pid> ... filter by <pid>
+  +fg ........ show file flags for file descripros
+  -n ......... don't convert network addr to hostnames
+  -P ......... don't convert network port to service names
+  -i <@h[:p]>. show connections to h (hostname|ip addr) with optional port p
+  -s <p:s> ... in conjunction with '-i' filter for protocol <p> in state <s>
+  -U ......... show unix domain sockets ('@' indicates abstract sock name, see unix(7))
+```
+
+```markdown
+file flags:
+  R/W/RW ..... read/write/read-write
+  CR ......... create
+  AP ......... append
+  TR ......... truncate
+```
+
+```markdown
+-s protocols
+  TCP, UDP
+
+-s states (TCP)
+  CLOSED, IDLE, BOUND, LISTEN, ESTABLISHED, SYN_SENT, SYN_RCDV, ESTABLISHED,
+  CLOSE_WAIT, FIN_WAIT1, CLOSING, LAST_ACK, FIN_WAIT_2, TIME_WAIT
+
+-s states (UDP)
+  Unbound, Idle
+```
+
+# Examples
+
+## File flags
+Show open files with file flags for process:
+```markdown
+lsof +fg -p <pid>
+```
+
+## Open TCP connections
+Show open tcp connections for `$USER`:
+```markdown
+lsof -a -u $USER -i TCP
+```
+**Note**: `-a` _ands_ the results. If `-a` is not given all open files matching
+`$USER` and all tcp connections are listed (_ored_).
+
+## Open connection to specific host
+Show open connections to `localhost` for `$USER`:
+```markdown
+lsof -a -u $USER -i @localhost
+```
+
+## Open connection to specific port
+Show open connections to port `:1234` for `$USER`:
+```markdown
+lsof -a -u $USER -i :1234
+```
+
+## IPv4 TCP connections in `ESTABLISHED` state
+```markdown
+lsof -i 4TCP -s TCP:ESTABLISHED
+```
+## List open files in a mounted directory.
+This may help to find which processes keep devices busy when trying to unmount
+and the device is currently busy.
+```markdown
+# Assuming /proc is a mount point.
+lsof /proc
+```