From 4b3f684d33af7459024011a06704cf4ca85dd0a3 Mon Sep 17 00:00:00 2001 From: Alvar Penning Date: Mon, 15 Sep 2025 22:20:08 +0200 Subject: check_by_ssh: Ignore output on stderr by default check_by_ssh no longer returns UNKNOWN if ssh(1) returns data on stderr. But it can be enforced again by the new "--unknown-on-stderr" option. --- The default logic of check_by_ssh results in an UNKNOWN state if the ssh(1) process produces output on stderr. Using the "--skip-stderr=[n]" option allows ignoring a certain amount of lines or disabling this check altogether. Furthermore, passing the "--warn-on-stderr" option reduces the exit code to WARNING. The "--help" output does not document this behavior, only states that "--warn-on-stderr" will result in the WARNING, but does not mention the UNKNOWN by default. The man page of ssh(1) mentions that debug information is logged to stderr. This conflicts with the described logic, resulting in check_by_ssh to go UNKNOWN, unless additional options are set. Starting with OpenSSH version 10.1, ssh(1) will report warnings to stderr if the opposite server does not support post-quantum cryptography, . This change, slowly being rolled out throughout the next months/years, might result in mass-breakages of check_by_ssh. By introducing a new "--unknown-on-stderr" option, enforcing the prior default logic of an UNKNOWN state for data on stderr, and ignoring output on stderr by default, check_by_ssh will continue to work. One might even argue that this change converges actual implementation and the documented behavior, as argued above. --- $ ssh example '/usr/lib/nagios/plugins/check_dummy 0 demo' ** WARNING: connection is not using a post-quantum key exchange algorithm. ** This session may be vulnerable to "store now, decrypt later" attacks. ** The server may need to be upgraded. See https://openssh.com/pq.html OK: demo $ echo $? 0 $ ./check_by_ssh -H example -C '/usr/lib/nagios/plugins/check_dummy 0 demo' OK: demo $ echo $? 0 $ ./check_by_ssh -H example -C '/usr/lib/nagios/plugins/check_dummy 0 demo' --warn-on-stderr Remote command execution failed: ** WARNING: connection is not using a post-quantum key exchange algorithm. $ echo $? 1 $ ./check_by_ssh -H example -C '/usr/lib/nagios/plugins/check_dummy 0 demo' --unknown-on-stderr Remote command execution failed: ** WARNING: connection is not using a post-quantum key exchange algorithm. $ echo $? 3 --- Fixes #2147. --- plugins/check_by_ssh.d/config.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'plugins/check_by_ssh.d') diff --git a/plugins/check_by_ssh.d/config.h b/plugins/check_by_ssh.d/config.h index 05435def..0e4b56d4 100644 --- a/plugins/check_by_ssh.d/config.h +++ b/plugins/check_by_ssh.d/config.h @@ -21,6 +21,7 @@ typedef struct { command_construct cmd; bool unknown_timeout; + bool unknown_on_stderr; bool warn_on_stderr; int skip_stdout; int skip_stderr; @@ -46,6 +47,7 @@ check_by_ssh_config check_by_ssh_config_init() { }, .unknown_timeout = false, + .unknown_on_stderr = false, .warn_on_stderr = false, .skip_stderr = 0, .skip_stdout = 0, -- cgit v1.2.3-74-g34f1 From e77ce530c44178521b7e0c4012feed1e8006e41e Mon Sep 17 00:00:00 2001 From: Lorenz Kästle <12514511+RincewindsHat@users.noreply.github.com> Date: Sun, 16 Nov 2025 14:32:03 +0100 Subject: check_by_ssh: Implement modern output functionality --- plugins/check_by_ssh.c | 184 +++++++++++++++++++++++++++++----------- plugins/check_by_ssh.d/config.h | 21 ++++- 2 files changed, 152 insertions(+), 53 deletions(-) (limited to 'plugins/check_by_ssh.d') diff --git a/plugins/check_by_ssh.c b/plugins/check_by_ssh.c index a43c0d34..ad385fbd 100644 --- a/plugins/check_by_ssh.c +++ b/plugins/check_by_ssh.c @@ -26,16 +26,17 @@ * *****************************************************************************/ -const char *progname = "check_by_ssh"; -const char *copyright = "2000-2024"; -const char *email = "devel@monitoring-plugins.org"; - #include "common.h" +#include "output.h" #include "utils.h" #include "utils_cmd.h" #include "check_by_ssh.d/config.h" #include "states.h" +const char *progname = "check_by_ssh"; +const char *copyright = "2000-2024"; +const char *email = "devel@monitoring-plugins.org"; + #ifndef NP_MAXARGS # define NP_MAXARGS 1024 #endif @@ -71,6 +72,10 @@ int main(int argc, char **argv) { const check_by_ssh_config config = tmp_config.config; + if (config.output_format_is_set) { + mp_set_format(config.output_format); + } + /* Set signal handling and alarm timeout */ if (signal(SIGALRM, timeout_alarm_handler) == SIG_ERR) { usage_va(_("Cannot catch SIGALRM")); @@ -85,62 +90,101 @@ int main(int argc, char **argv) { } } - output chld_out; - output chld_err; - mp_state_enum result = cmd_run_array(config.cmd.commargv, &chld_out, &chld_err, 0); + cmd_run_result child_result = cmd_run_array2(config.cmd.commargv, 0); + mp_check overall = mp_check_init(); /* SSH returns 255 if connection attempt fails; include the first line of error output */ - if (result == 255 && config.unknown_timeout) { - printf(_("SSH connection failed: %s\n"), - chld_err.lines > 0 ? chld_err.line[0] : "(no error output)"); - return STATE_UNKNOWN; + mp_subcheck sc_ssh_execution = mp_subcheck_init(); + if (child_result.cmd_error_code == 255 && config.unknown_timeout) { + xasprintf(&sc_ssh_execution.output, "SSH connection failed: %s", + child_result.stderr.lines > 0 ? child_result.stderr.line[0] + : "(no error output)"); + + sc_ssh_execution = mp_set_subcheck_state(sc_ssh_execution, STATE_UNKNOWN); + mp_add_subcheck_to_check(&overall, sc_ssh_execution); + mp_exit(overall); } + xasprintf(&sc_ssh_execution.output, "SSH connection succeeded"); + sc_ssh_execution = mp_set_subcheck_state(sc_ssh_execution, STATE_OK); + mp_add_subcheck_to_check(&overall, sc_ssh_execution); if (verbose) { - for (size_t i = 0; i < chld_out.lines; i++) { - printf("stdout: %s\n", chld_out.line[i]); + for (size_t i = 0; i < child_result.stdout.lines; i++) { + printf("stdout: %s\n", child_result.stdout.line[i]); } - for (size_t i = 0; i < chld_err.lines; i++) { - printf("stderr: %s\n", chld_err.line[i]); + for (size_t i = 0; i < child_result.stderr.lines; i++) { + printf("stderr: %s\n", child_result.stderr.line[i]); } } size_t skip_stdout = 0; - if (config.skip_stdout == -1) { /* --skip-stdout specified without argument */ - skip_stdout = chld_out.lines; + if (config.skip_stdout) { /* --skip-stdout specified without argument */ + skip_stdout = child_result.stdout.lines; } else { - skip_stdout = config.skip_stdout; + skip_stdout = config.stdout_lines_to_ignore; } size_t skip_stderr = 0; - if (config.skip_stderr == -1) { /* --skip-stderr specified without argument */ - skip_stderr = chld_err.lines; + if (config.skip_stderr) { /* --skip-stderr specified without argument */ + skip_stderr = child_result.stderr.lines; } else { - skip_stderr = config.skip_stderr; + skip_stderr = config.sterr_lines_to_ignore; } /* Allow UNKNOWN or WARNING state for (non-skipped) output found on stderr */ - if (chld_err.lines > (size_t)skip_stderr && (config.unknown_on_stderr || config.warn_on_stderr)) { - printf(_("Remote command execution failed: %s\n"), chld_err.line[skip_stderr]); + if (child_result.stderr.lines > skip_stderr && + (config.unknown_on_stderr || config.warn_on_stderr)) { + mp_subcheck sc_stderr = mp_subcheck_init(); + xasprintf(&sc_stderr.output, "remote command execution failed: %s", + child_result.stderr.line[skip_stderr]); + if (config.unknown_on_stderr) { - return max_state_alt(result, STATE_UNKNOWN); - } else if (config.warn_on_stderr) { - return max_state_alt(result, STATE_WARNING); + sc_stderr = mp_set_subcheck_state(sc_stderr, STATE_UNKNOWN); + } + + if (config.warn_on_stderr) { + sc_stderr = mp_set_subcheck_state(sc_stderr, STATE_WARNING); } + + mp_add_subcheck_to_check(&overall, sc_stderr); + // TODO still exit here? } /* this is simple if we're not supposed to be passive. * Wrap up quickly and keep the tricks below */ if (!config.passive) { - if (chld_out.lines > (size_t)skip_stdout) { - for (size_t i = skip_stdout; i < chld_out.lines; i++) { - puts(chld_out.line[i]); + mp_subcheck sc_active_check = mp_subcheck_init(); + xasprintf(&sc_active_check.output, "command stdout:"); + + if (child_result.stdout.lines > skip_stdout) { + for (size_t i = skip_stdout; i < child_result.stdout.lines; i++) { + xasprintf(&sc_active_check.output, "%s\n%s", sc_active_check.output, + child_result.stdout.line[i]); } } else { - printf(_("%s - check_by_ssh: Remote command '%s' returned status %d\n"), - state_text(result), config.remotecmd, result); + xasprintf(&sc_active_check.output, "remote command '%s' returned status %d", + config.remotecmd, child_result.cmd_error_code); + } + + /* return error status from remote command */ + + switch (child_result.cmd_error_code) { + case 0: + sc_active_check = mp_set_subcheck_state(sc_active_check, STATE_OK); + break; + case 1: + sc_active_check = mp_set_subcheck_state(sc_active_check, STATE_WARNING); + break; + case 2: + sc_active_check = mp_set_subcheck_state(sc_active_check, STATE_CRITICAL); + break; + default: + sc_active_check = mp_set_subcheck_state(sc_active_check, STATE_UNKNOWN); + break; } - return result; /* return error status from remote command */ + + mp_add_subcheck_to_check(&overall, sc_active_check); + mp_exit(overall); } /* @@ -148,36 +192,57 @@ int main(int argc, char **argv) { */ /* process output */ - FILE *file_pointer = NULL; - if (!(file_pointer = fopen(config.outputfile, "a"))) { - printf(_("SSH WARNING: could not open %s\n"), config.outputfile); - exit(STATE_UNKNOWN); + mp_subcheck sc_passive_file = mp_subcheck_init(); + FILE *output_file = NULL; + if (!(output_file = fopen(config.outputfile, "a"))) { + xasprintf(&sc_passive_file.output, "could not open %s", config.outputfile); + sc_passive_file = mp_set_subcheck_state(sc_passive_file, STATE_UNKNOWN); + + mp_add_subcheck_to_check(&overall, sc_passive_file); + mp_exit(overall); } + xasprintf(&sc_passive_file.output, "opened output file %s", config.outputfile); + sc_passive_file = mp_set_subcheck_state(sc_passive_file, STATE_OK); + mp_add_subcheck_to_check(&overall, sc_passive_file); + time_t local_time = time(NULL); unsigned int commands = 0; char *status_text; int cresult; - for (size_t i = skip_stdout; i < chld_out.lines; i++) { - status_text = chld_out.line[i++]; - if (i == chld_out.lines || strstr(chld_out.line[i], "STATUS CODE: ") == NULL) { - die(STATE_UNKNOWN, _("%s: Error parsing output\n"), progname); + mp_subcheck sc_parse_passive = mp_subcheck_init(); + for (size_t i = skip_stdout; i < child_result.stdout.lines; i++) { + status_text = child_result.stdout.line[i++]; + if (i == child_result.stdout.lines || + strstr(child_result.stdout.line[i], "STATUS CODE: ") == NULL) { + + sc_parse_passive = mp_set_subcheck_state(sc_parse_passive, STATE_UNKNOWN); + xasprintf(&sc_parse_passive.output, "failed to parse output"); + mp_add_subcheck_to_check(&overall, sc_parse_passive); + mp_exit(overall); } if (config.service[commands] && status_text && - sscanf(chld_out.line[i], "STATUS CODE: %d", &cresult) == 1) { - fprintf(file_pointer, "[%d] PROCESS_SERVICE_CHECK_RESULT;%s;%s;%d;%s\n", - (int)local_time, config.host_shortname, config.service[commands++], cresult, - status_text); + sscanf(child_result.stdout.line[i], "STATUS CODE: %d", &cresult) == 1) { + fprintf(output_file, "[%d] PROCESS_SERVICE_CHECK_RESULT;%s;%s;%d;%s\n", (int)local_time, + config.host_shortname, config.service[commands++], cresult, status_text); } } + sc_parse_passive = mp_set_subcheck_state(sc_parse_passive, STATE_OK); + xasprintf(&sc_parse_passive.output, "parsed and wrote output"); + mp_add_subcheck_to_check(&overall, sc_parse_passive); + /* Multiple commands and passive checking should always return OK */ - exit(result); + mp_exit(overall); } /* process command-line arguments */ check_by_ssh_config_wrapper process_arguments(int argc, char **argv) { + enum { + output_format_index = CHAR_MAX + 1, + }; + static struct option longopts[] = { {"version", no_argument, 0, 'V'}, {"help", no_argument, 0, 'h'}, @@ -207,6 +272,7 @@ check_by_ssh_config_wrapper process_arguments(int argc, char **argv) { {"ssh-option", required_argument, 0, 'o'}, {"quiet", no_argument, 0, 'q'}, {"configfile", optional_argument, 0, 'F'}, + {"output-format", required_argument, 0, output_format_index}, {0, 0, 0, 0}}; check_by_ssh_config_wrapper result = { @@ -327,20 +393,27 @@ check_by_ssh_config_wrapper process_arguments(int argc, char **argv) { break; case 'S': /* skip n (or all) lines on stdout */ if (optarg == NULL) { - result.config.skip_stdout = -1; /* skip all output on stdout */ + result.config.skip_stdout = true; /* skip all output on stdout */ + + if (verbose) { + printf("Setting the skip_stdout flag\n"); + } } else if (!is_integer(optarg)) { usage_va(_("skip-stdout argument must be an integer")); } else { - result.config.skip_stdout = atoi(optarg); + result.config.stdout_lines_to_ignore = atoi(optarg); } break; case 'E': /* skip n (or all) lines on stderr */ if (optarg == NULL) { - result.config.skip_stderr = -1; /* skip all output on stderr */ + result.config.skip_stderr = true; /* skip all output on stderr */ + if (verbose) { + printf("Setting the skip_stderr flag\n"); + } } else if (!is_integer(optarg)) { usage_va(_("skip-stderr argument must be an integer")); } else { - result.config.skip_stderr = atoi(optarg); + result.config.sterr_lines_to_ignore = atoi(optarg); } break; case 'e': /* exit with unknown if there is an output on stderr */ @@ -360,6 +433,18 @@ check_by_ssh_config_wrapper process_arguments(int argc, char **argv) { result.config.cmd = comm_append(result.config.cmd, "-F"); result.config.cmd = comm_append(result.config.cmd, optarg); break; + case output_format_index: { + parsed_output_format parser = mp_parse_output_format(optarg); + if (!parser.parsing_success) { + // TODO List all available formats here, maybe add anothoer usage function + printf("Invalid output format: %s\n", optarg); + exit(STATE_UNKNOWN); + } + + result.config.output_format_is_set = true; + result.config.output_format = parser.output_format; + break; + } default: /* help */ usage5(); } @@ -502,6 +587,7 @@ void print_help(void) { printf(" %s\n", "-U, --unknown-timeout"); printf(" %s\n", _("Make connection problems return UNKNOWN instead of CRITICAL")); printf(UT_VERBOSE); + printf(UT_OUTPUT_FORMAT); printf("\n"); printf(" %s\n", _("The most common mode of use is to refer to a local identity file with")); printf(" %s\n", _("the '-i' option. In this mode, the identity pair should have a null")); diff --git a/plugins/check_by_ssh.d/config.h b/plugins/check_by_ssh.d/config.h index 0e4b56d4..b6a57964 100644 --- a/plugins/check_by_ssh.d/config.h +++ b/plugins/check_by_ssh.d/config.h @@ -1,6 +1,7 @@ #pragma once #include "../../config.h" +#include "output.h" #include typedef struct { @@ -23,10 +24,16 @@ typedef struct { bool unknown_timeout; bool unknown_on_stderr; bool warn_on_stderr; - int skip_stdout; - int skip_stderr; + bool skip_stdout; + size_t stdout_lines_to_ignore; + bool skip_stderr; + size_t sterr_lines_to_ignore; + bool passive; char *outputfile; + + bool output_format_is_set; + mp_output_format output_format; } check_by_ssh_config; check_by_ssh_config check_by_ssh_config_init() { @@ -49,10 +56,16 @@ check_by_ssh_config check_by_ssh_config_init() { .unknown_timeout = false, .unknown_on_stderr = false, .warn_on_stderr = false, - .skip_stderr = 0, - .skip_stdout = 0, + + .skip_stderr = false, + .stdout_lines_to_ignore = 0, + .skip_stdout = false, + .sterr_lines_to_ignore = 0, + .passive = false, .outputfile = NULL, + + .output_format_is_set = false, }; return tmp; } -- cgit v1.2.3-74-g34f1