ifalive − check network interface activity
ifalive −i [−dnp] IFACE [PID]
ifalive [−c] [−dn] [−s SIG] PID [EXPR...]
ifalive −r [−dnp] [PID]
Given the network interface name and the PID of the program that controls it, ifalive checks if the interface is "alive", and if not, terminates the program.
It is designed as an ancillary utility for jumper(8), to help automatically shut down inactive interfaces.
The program runs in three different operation modes, selected by the options −i, −c, and −r.
The −i option requests initialization mode. In this mode, ifalive remembers information about the network interface, and the PID of the corresponding process that controls it.
If the PID argument is not given, the program assumes the PID of its parent process. The −p option, if used, instructs the program to use PID of the parent process of the originally obtained PID. For example,
ifalive -i -p tun0 1822
means that interface tun0 is controlled by the parent of PID 1822, whereas
ifalive -i -p tun0
means that it is controlled by the grand-parent of ifalive itself. This option can be used multiple times to move up the process ancestor tree. For example,
ifalive -i -ppp tun0 1822
means use grand-grand-parent of PID 1822.
The information is stored in a disk file /var/run/ifalive/PID. This file will then be used to store intermediate information about the state of the interface.
The initialization is normally performed right after the corresponding interface is started. For example, supposing the interface is controlled by vpnc(8), the following line should appear in the /etc/vpnc/vpnc-script-post-connect-action file:
/usr/libexec/ifalive -i -pp $TUNDEV
This is the main (and the default) operation mode. It is requested by the −c option, or by the absence of the mode specifying option. The PID argument is required. The tool will first look up the interface name corresponding to that PID, and will evaluate the expression EXPR to check if the interface is active. In the absence of EXPR, the default expression is evaluated. See the section EXPRESSION, for the description.
If the expression evaluates to true, the utility will update the interface statistics in its spool file, and will exit. Otherwise, it will terminate the controlling program by sending the SIGTERM signal to PID.
The check mode is normally run periodically in a HEARTBEAT event:
command "/usr/libexec/ifalive -c $pid";
The cleanup mode is requested by the −r command line option. In this mode, ifalive removes the state file for the given PID. The actual PID is computed as described in subsection Initialization, above.
This mode should be run when the interface goes down. For example, if the interface is controlled by vpnc, the following line should appear in the file /etc/vpnc/vpnc-script-post-disconnect-action:
/usr/libexec/ifalive -r -pp
operates on two variables: the previous interface state
a, and its current state, b. Both variables
have a number of numeric attributes, which are accessed as
X.attr, where X stands for the
variable and attr for the attribute name. The
following attributes are defined:
Number of bytes received.
Number of network packets received.
Number of errors while receiving.
Number of dropped incoming (received) packets.
Number of FIFO errors on incoming packets.
Number of received frame errors.
Number of received compressed format packets.
Number of received multicast packets.
Number of bytes transmitted.
Number of network packets transmitted.
Number of transmit errors.
Number of dropped transmit packets.
Number of FIFO errors on transmit.
Number of collisions.
Number of carrier errors.
Number of transmitted compressed format packets.
The usual arithmetical operations (+, −, *, /) are allowed over these values and integer numeric constants. The results can be compared using the operators: == (or ==), !=, <, <=, >, >=. The comparisons can be combined using boolean operations or and and. Logical values are negated using !. The following table lists the operators in order of their precedence. Operators down the table are executed prior to those located above. Operators on the same line are executed left to right.
=, ==, !=
<, <=, >, >=
unary !, unary −
Braces can be used to control the precedence.
The default expression is:
a.rx_bytes != b.rx_bytes and a.tx_bytes != b.tx_bytes
It means that interface is considered alive if some bytes were transmitted or received over it since the last check.
Initializes the state file.
Checks the state of the link (the default).
Removes the state file for PID
Displays a help summary.
Enable debug output.
Dry-run mode: print everything, do nothing.
Use parent of PID (grand-parent for −pp, etc.)
Terminate idle process with signal SIG, instead of the default SIGTERM.
Network interface statistics.
Directory where interface state files are stored. Files are named by the corresponding PID.
The program is Linux-specific.
Report bugs to <bug−firstname.lastname@example.org>.
© 2017 Sergey Poznyakoff
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.
Manpage server at Ulysses.gnu.org.ua.
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