Option --follow-new (-W) works the same as --follow (-w) but initially
seeks to the end of kernel ring buffer, so it prints only new messages.
Useful for capturing kernel messages during actions without past log.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
---
bash-completion/dmesg | 1 +
sys-utils/dmesg.1 | 3 +++
sys-utils/dmesg.c | 11 +++++++++--
3 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/bash-completion/dmesg b/bash-completion/dmesg
index 319605f8ee39..02f2fc7a62d4 100644
--- a/bash-completion/dmesg
+++ b/bash-completion/dmesg
@@ -55,6 +55,7 @@ _dmesg_module()
--time-format
--userspace
--follow
+ --follow-new
--decode
--help
--version"
diff --git a/sys-utils/dmesg.1 b/sys-utils/dmesg.1
index 31bfb56f3f5e..61a6ce89465d 100644
--- a/sys-utils/dmesg.1
+++ b/sys-utils/dmesg.1
@@ -193,6 +193,9 @@ Print userspace messages.
Wait for new messages. This feature is supported only on systems with
a readable /dev/kmsg (since kernel 3.5.0).
.TP
+.BR \-W , " \-\-follow-new"
+Wait and print only new messages.
+.TP
.BR \-x , " \-\-decode"
Decode facility and level (priority) numbers to human-readable prefixes.
.TP
diff --git a/sys-utils/dmesg.c b/sys-utils/dmesg.c
index 1eb7cde3c1b2..ae1ebc74a2d9 100644
--- a/sys-utils/dmesg.c
+++ b/sys-utils/dmesg.c
@@ -190,6 +190,7 @@ struct dmesg_control {
unsigned int time_fmt; /* time format */
unsigned int follow:1, /* wait for new messages */
+ end:1, /* seek to the of buffer */
raw:1, /* raw mode */
noesc:1, /* no escape */
fltr_lev:1, /* filter out by levels[] */
@@ -292,6 +293,7 @@ static void __attribute__((__noreturn__)) usage(void)
fputs(_(" -s, --buffer-size <size> buffer size to query the kernel ring buffer\n"), out);
fputs(_(" -u, --userspace display userspace messages\n"), out);
fputs(_(" -w, --follow wait for new messages\n"), out);
+ fputs(_(" -W, --follow-new wait and print only new messages\n"), out);
fputs(_(" -x, --decode decode facility and level to readable string\n"), out);
fputs(_(" -d, --show-delta show time delta between printed messages\n"), out);
fputs(_(" -e, --reltime show local time and time delta in readable format\n"), out);
@@ -1127,7 +1129,7 @@ static int init_kmsg(struct dmesg_control *ctl)
*
* ... otherwise SYSLOG_ACTION_CLEAR will have no effect for kmsg.
*/
- lseek(ctl->kmsg, 0, SEEK_DATA);
+ lseek(ctl->kmsg, 0, ctl->end ? SEEK_END : SEEK_DATA);
/*
* Old kernels (<3.5) allow to successfully open /dev/kmsg for
@@ -1336,6 +1338,7 @@ int main(int argc, char *argv[])
{ "file", required_argument, NULL, 'F' },
{ "facility", required_argument, NULL, 'f' },
{ "follow", no_argument, NULL, 'w' },
+ { "follow-new", no_argument, NULL, 'W' },
{ "human", no_argument, NULL, 'H' },
{ "help", no_argument, NULL, 'h' },
{ "kernel", no_argument, NULL, 'k' },
@@ -1375,7 +1378,7 @@ int main(int argc, char *argv[])
textdomain(PACKAGE);
close_stdout_atexit();
- while ((c = getopt_long(argc, argv, "CcDdEeF:f:HhkL::l:n:iPprSs:TtuVwx",
+ while ((c = getopt_long(argc, argv, "CcDdEeF:f:HhkL::l:n:iPprSs:TtuVWwx",
longopts, NULL)) != -1) {
err_exclusive_options(c, longopts, excl, excl_st);
@@ -1466,6 +1469,10 @@ int main(int argc, char *argv[])
case 'w':
ctl.follow = 1;
break;
+ case 'W':
+ ctl.follow = 1;
+ ctl.end = 1;
+ break;
case 'x':
ctl.decode = 1;
break;
